diff --git a/src/evaluator.rs b/src/evaluator.rs
index 6212469..7c470c8 100644
--- a/src/evaluator.rs
+++ b/src/evaluator.rs
@@ -279,6 +279,9 @@ fn evaluate_node(ast_node: &AstNode) -> Result<Number, String> {
 mod tests {
 	use crate::eval;
 	use super::*;
+	use crate::currency;
+	use crate::extra_units;
+	use crate::units::UnitType;
 
 	fn eval_default<'a>(input: &'a str) -> Number {
 		let result = eval(input, true, false).unwrap();
@@ -336,4 +339,57 @@ mod tests {
 		assert_eq!(eval_num("sin(2)"), "0.9092974268256816953960198659117448427");
 		assert_eq!(eval_num("sin(-2)"), "-0.9092974268256816953960198659117448427");
 	}
+
+	#[test]
+	fn test_divide_currency_and_mass_by_volume() {
+		// Ensure a clean registry so the IDs are deterministic
+		extra_units::clear_for_tests();
+
+		// Minimal rates (USD base). 1 USD = 7.07 CNY
+		let json = r#"{"base":"USD","rates":{"USD":1,"CNY":7.07}}"#;
+		currency::register_currencies_from_exchange_rate_api_json(json).unwrap();
+
+		let x = eval_default("5.55 usd / 64 fl oz");
+		assert_eq!(x.unit.category(), UnitType::CurrencyPerVolume);
+		assert_eq!(x.unit.singular(), "USD/floz");
+
+		let y = eval_default("5.55 g / 64 fl oz");
+		assert_eq!(y.unit.category(), UnitType::MassPerVolume);
+		assert_eq!(y.unit.singular(), "g/floz");
+
+		// Conversion should work on the derived units:
+		let z = eval_default("5.55 usd / 64 fl oz to cny/l");
+		assert_eq!(z.unit.singular(), "CNY/l");
+
+		let w = eval_default("5.55 g / 64 fl oz to g/ml");
+		assert_eq!(w.unit.singular(), "g/ml");
+	}
+
+	#[test]
+	fn test_multiply_cancels_derived_units() {
+		extra_units::clear_for_tests();
+
+		let json = r#"{"base":"USD","rates":{"USD":1,"CNY":7.07}}"#;
+		currency::register_currencies_from_exchange_rate_api_json(json).unwrap();
+
+		// Your example: (USD/L) * floz -> USD
+		let out = eval_default("(1.48-1/3) usd / 1.25 l * 144 fl oz");
+		assert_eq!(out.unit.category(), UnitType::Currency);
+		assert_eq!(out.unit.singular(), "USD");
+		assert!(!out.value.is_nan());
+
+		let assert_close = |actual: D128, expected: D128| {
+			// Derived unit weights use division, so allow tiny rounding differences.
+			assert!((actual - expected).abs() < d!(1e-24));
+		};
+
+		// Cancellation sanity checks
+		let usd_back = eval_default("5.55 usd / 64 fl oz * 64 fl oz");
+		assert_eq!(usd_back.unit.singular(), "USD");
+		assert_close(usd_back.value, d!(5.55));
+
+		let g_back = eval_default("5.55 g / 64 fl oz * 64 fl oz");
+		assert_eq!(g_back.unit.singular(), "gram");
+		assert_close(g_back.value, d!(5.55));
+	}
 }
diff --git a/src/lexer.rs b/src/lexer.rs
index 374aa81..5157ba8 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -909,7 +909,10 @@ pub fn lex(input: &str, remove_trailing_operator: bool) -> Result<Vec<Token>, St
 				(Token::LexerKeyword(Revolution), Token::LexerKeyword(Per), Token::Unit(Minute)) => {
 					tokens[token_index-2] = Token::Unit(RevolutionsPerMinute);
 				},
-				// currency per {mass|volume|length|area}, for example usd/lb, cny/kg, usd/l, usd/m, usd/m2
+				// composite units:
+				// - currency per {mass|volume|length|area} (usd/lb, cny/kg, usd/l, usd/m, usd/m2)
+				// - mass per volume (g/ml, kg/l, lb/gal)
+				// - volume per mass (ml/g, l/kg)
 				(Token::Unit(left_u), Token::LexerKeyword(Per), Token::Unit(right_u)) => {
 					let left_cat = left_u.category();
 					let right_cat = right_u.category();
@@ -1002,6 +1005,86 @@ pub fn lex(input: &str, remove_trailing_operator: bool) -> Result<Vec<Token>, St
 							weight,
 						);
 						tokens[token_index-2] = Token::Unit(composite);
+					} else if left_cat == UnitType::Mass && right_cat == UnitType::Volume {
+						let mass_abbrev: &str = match *left_u {
+							Milligram => "mg",
+							Gram => "g",
+							Hectogram => "hg",
+							Kilogram => "kg",
+							MetricTon => "t",
+							Ounce => "oz",
+							Pound => "lb",
+							Stone => "st",
+							ShortTon => "ston",
+							LongTon => "lton",
+							_ => left_u.singular(),
+						};
+						let vol_abbrev: &str = match *right_u {
+							Milliliter => "ml",
+							Centiliter => "cl",
+							Deciliter => "dl",
+							Liter => "l",
+							Teaspoon => "tsp",
+							Tablespoon => "tbsp",
+							FluidOunce => "floz",
+							Cup => "cup",
+							Pint => "pt",
+							Quart => "qt",
+							Gallon => "gal",
+							OilBarrel => "bbl",
+							_ => right_u.singular(),
+						};
+						let display = format!("{}/{}", mass_abbrev, vol_abbrev);
+						let key = format!("{mass_abbrev}_per_{vol_abbrev}");
+						let weight = left_u.weight() / right_u.weight(); // grams per cubic-mm
+						let composite = extra_units::upsert_unit(
+							&key,
+							&display,
+							&display,
+							UnitType::MassPerVolume,
+							weight,
+						);
+						tokens[token_index-2] = Token::Unit(composite);
+					} else if left_cat == UnitType::Volume && right_cat == UnitType::Mass {
+						let vol_abbrev: &str = match *left_u {
+							Milliliter => "ml",
+							Centiliter => "cl",
+							Deciliter => "dl",
+							Liter => "l",
+							Teaspoon => "tsp",
+							Tablespoon => "tbsp",
+							FluidOunce => "floz",
+							Cup => "cup",
+							Pint => "pt",
+							Quart => "qt",
+							Gallon => "gal",
+							OilBarrel => "bbl",
+							_ => left_u.singular(),
+						};
+						let mass_abbrev: &str = match *right_u {
+							Milligram => "mg",
+							Gram => "g",
+							Hectogram => "hg",
+							Kilogram => "kg",
+							MetricTon => "t",
+							Ounce => "oz",
+							Pound => "lb",
+							Stone => "st",
+							ShortTon => "ston",
+							LongTon => "lton",
+							_ => right_u.singular(),
+						};
+						let display = format!("{}/{}", vol_abbrev, mass_abbrev);
+						let key = format!("{vol_abbrev}_per_{mass_abbrev}");
+						let weight = left_u.weight() / right_u.weight(); // cubic-mm per gram
+						let composite = extra_units::upsert_unit(
+							&key,
+							&display,
+							&display,
+							UnitType::VolumePerMass,
+							weight,
+						);
+						tokens[token_index-2] = Token::Unit(composite);
 					} else {
 						replaced = false;
 					}
diff --git a/src/units.rs b/src/units.rs
index 0b1968b..cf2f106 100644
--- a/src/units.rs
+++ b/src/units.rs
@@ -50,6 +50,10 @@ pub enum UnitType {
 	CurrencyPerLength,
 	/// A currency-per-area unit, for example USD/m2 or EUR/ft2
 	CurrencyPerArea,
+	/// A mass-per-volume unit (density / concentration), e.g. g/ml
+	MassPerVolume,
+	/// A volume-per-mass unit (specific volume), e.g. ml/g
+	VolumePerMass,
 }
 use UnitType::*;
 
@@ -566,6 +570,49 @@ pub fn multiply(left: Number, right: Number) -> Result<Number, String> {
 	actual_multiply(left, right, false)
 }
 
+fn parse_currency_numerator(unit: Unit) -> Option<Unit> {
+	let code_lower = unit.singular().split('/').next()?.to_ascii_lowercase();
+	extra_units::lookup_unit(&code_lower)
+}
+
+fn parse_mass_numerator(unit: Unit) -> Option<Unit> {
+	let s = unit.singular().split('/').next()?.to_ascii_lowercase();
+	let u = match s.as_str() {
+		"mg" => Milligram,
+		"g" => Gram,
+		"hg" => Hectogram,
+		"kg" => Kilogram,
+		"t" => MetricTon,
+		"oz" => Ounce,
+		"lb" => Pound,
+		"st" => Stone,
+		"ston" => ShortTon,
+		"lton" => LongTon,
+		_ => return None,
+	};
+	Some(u)
+}
+
+fn parse_volume_numerator(unit: Unit) -> Option<Unit> {
+	let s = unit.singular().split('/').next()?.to_ascii_lowercase();
+	let u = match s.as_str() {
+		"ml" => Milliliter,
+		"cl" => Centiliter,
+		"dl" => Deciliter,
+		"l" => Liter,
+		"tsp" => Teaspoon,
+		"tbsp" => Tablespoon,
+		"floz" => FluidOunce,
+		"cup" => Cup,
+		"pt" => Pint,
+		"qt" => Quart,
+		"gal" => Gallon,
+		"bbl" => OilBarrel,
+		_ => return None,
+	};
+	Some(u)
+}
+
 fn actual_multiply(left: Number, right: Number, swapped: bool) -> Result<Number, String> {
 	let lcat = left.unit.category();
 	let rcat = right.unit.category();
@@ -645,6 +692,81 @@ fn actual_multiply(left: Number, right: Number, swapped: bool) -> Result<Number,
 		};
 		let data_storage = Number::new(result, Bit);
 		Ok(convert(data_storage, final_unit)?)
+	} else if lcat == CurrencyPerVolume && rcat == Volume {
+		// (currency per volume) * volume = currency
+		let rate_usd_per_mm3 = left.value * left.unit.weight();
+		let volume_mm3 = right.value * right.unit.weight();
+		let usd_amount = rate_usd_per_mm3 * volume_mm3;
+
+		let usd_unit = extra_units::lookup_unit("usd")
+			.ok_or("Currency rates not initialized (missing USD)")?;
+
+		let mut result = Number::new(usd_amount, usd_unit);
+		if let Some(cur_unit) = parse_currency_numerator(left.unit) {
+			result = convert(result, cur_unit)?;
+		}
+		Ok(result)
+	} else if lcat == CurrencyPerMass && rcat == Mass {
+		let rate_usd_per_g = left.value * left.unit.weight();
+		let grams = right.value * right.unit.weight();
+		let usd_amount = rate_usd_per_g * grams;
+
+		let usd_unit = extra_units::lookup_unit("usd")
+			.ok_or("Currency rates not initialized (missing USD)")?;
+
+		let mut result = Number::new(usd_amount, usd_unit);
+		if let Some(cur_unit) = parse_currency_numerator(left.unit) {
+			result = convert(result, cur_unit)?;
+		}
+		Ok(result)
+	} else if lcat == CurrencyPerLength && rcat == Length {
+		let rate_usd_per_mm = left.value * left.unit.weight();
+		let mm = right.value * right.unit.weight();
+		let usd_amount = rate_usd_per_mm * mm;
+
+		let usd_unit = extra_units::lookup_unit("usd")
+			.ok_or("Currency rates not initialized (missing USD)")?;
+
+		let mut result = Number::new(usd_amount, usd_unit);
+		if let Some(cur_unit) = parse_currency_numerator(left.unit) {
+			result = convert(result, cur_unit)?;
+		}
+		Ok(result)
+	} else if lcat == CurrencyPerArea && rcat == Area {
+		let rate_usd_per_mm2 = left.value * left.unit.weight();
+		let mm2 = right.value * right.unit.weight();
+		let usd_amount = rate_usd_per_mm2 * mm2;
+
+		let usd_unit = extra_units::lookup_unit("usd")
+			.ok_or("Currency rates not initialized (missing USD)")?;
+
+		let mut result = Number::new(usd_amount, usd_unit);
+		if let Some(cur_unit) = parse_currency_numerator(left.unit) {
+			result = convert(result, cur_unit)?;
+		}
+		Ok(result)
+	} else if lcat == MassPerVolume && rcat == Volume {
+		// (mass per volume) * volume = mass
+		let rate_g_per_mm3 = left.value * left.unit.weight();
+		let volume_mm3 = right.value * right.unit.weight();
+		let grams = rate_g_per_mm3 * volume_mm3;
+
+		let mut result = Number::new(grams, Gram);
+		if let Some(mass_unit) = parse_mass_numerator(left.unit) {
+			result = convert(result, mass_unit)?;
+		}
+		Ok(result)
+	} else if lcat == VolumePerMass && rcat == Mass {
+		// (volume per mass) * mass = volume
+		let rate_mm3_per_g = left.value * left.unit.weight();
+		let grams = right.value * right.unit.weight();
+		let mm3 = rate_mm3_per_g * grams;
+
+		let mut result = Number::new(mm3, CubicMillimeter);
+		if let Some(vol_unit) = parse_volume_numerator(left.unit) {
+			result = convert(result, vol_unit)?;
+		}
+		Ok(result)
 	} else if lcat == Voltage && rcat == ElectricCurrent {
 		// 1 volt * 1 ampere = 1 watt
 		let result = (left.value * left.unit.weight()) * (right.value * right.unit.weight());
@@ -729,6 +851,201 @@ pub fn divide(left: Number, right: Number) -> Result<Number, String> {
 		let bits_per_second = convert(right, BitsPerSecond)?;
 		let seconds = Number::new(bits.value / bits_per_second.value, Second);
 		Ok(to_ideal_unit(seconds))
+	} else if lcat == Currency && rcat == Volume {
+		// 5 usd / 64 floz => usd/floz (convertible to usd/l, cny/l, etc)
+		let cur_upper = left.unit.singular().to_ascii_uppercase();
+		let cur_lower = cur_upper.to_ascii_lowercase();
+		let denom_abbrev: &str = match right.unit {
+			Milliliter => "ml",
+			Centiliter => "cl",
+			Deciliter => "dl",
+			Liter => "l",
+			Teaspoon => "tsp",
+			Tablespoon => "tbsp",
+			FluidOunce => "floz",
+			Cup => "cup",
+			Pint => "pt",
+			Quart => "qt",
+			Gallon => "gal",
+			OilBarrel => "bbl",
+			_ => right.unit.singular(),
+		};
+		let display = format!("{}/{}", cur_upper, denom_abbrev);
+		let key = format!("{cur_lower}_per_{denom_abbrev}");
+		let composite = crate::extra_units::upsert_unit(
+			&key,
+			&display,
+			&display,
+			CurrencyPerVolume,
+			left.unit.weight() / right.unit.weight(),
+		);
+		Ok(Number::new(left.value / right.value, composite))
+	} else if lcat == Currency && rcat == Mass {
+		// usd/kg etc
+		let cur_upper = left.unit.singular().to_ascii_uppercase();
+		let cur_lower = cur_upper.to_ascii_lowercase();
+		let denom_abbrev: &str = match right.unit {
+			Milligram => "mg",
+			Gram => "g",
+			Hectogram => "hg",
+			Kilogram => "kg",
+			MetricTon => "t",
+			Ounce => "oz",
+			Pound => "lb",
+			Stone => "st",
+			ShortTon => "ston",
+			LongTon => "lton",
+			_ => right.unit.singular(),
+		};
+		let display = format!("{}/{}", cur_upper, denom_abbrev);
+		let key = format!("{cur_lower}_per_{denom_abbrev}");
+		let composite = crate::extra_units::upsert_unit(
+			&key,
+			&display,
+			&display,
+			CurrencyPerMass,
+			left.unit.weight() / right.unit.weight(),
+		);
+		Ok(Number::new(left.value / right.value, composite))
+	} else if lcat == Currency && rcat == Length {
+		// usd/m, etc
+		let cur_upper = left.unit.singular().to_ascii_uppercase();
+		let cur_lower = cur_upper.to_ascii_lowercase();
+		let denom_abbrev: &str = match right.unit {
+			Millimeter => "mm",
+			Centimeter => "cm",
+			Decimeter => "dm",
+			Meter => "m",
+			Kilometer => "km",
+			Inch => "in",
+			Foot => "ft",
+			Yard => "yd",
+			Mile => "mi",
+			NauticalMile => "nmi",
+			LightYear => "ly",
+			LightSecond => "lightsec",
+			_ => right.unit.singular(),
+		};
+		let display = format!("{}/{}", cur_upper, denom_abbrev);
+		let key = format!("{cur_lower}_per_{denom_abbrev}");
+		let composite = crate::extra_units::upsert_unit(
+			&key,
+			&display,
+			&display,
+			CurrencyPerLength,
+			left.unit.weight() / right.unit.weight(),
+		);
+		Ok(Number::new(left.value / right.value, composite))
+	} else if lcat == Currency && rcat == Area {
+		// usd/m2, etc
+		let cur_upper = left.unit.singular().to_ascii_uppercase();
+		let cur_lower = cur_upper.to_ascii_lowercase();
+		let denom_abbrev: &str = match right.unit {
+			SquareMillimeter => "mm2",
+			SquareCentimeter => "cm2",
+			SquareDecimeter => "dm2",
+			SquareMeter => "m2",
+			SquareKilometer => "km2",
+			SquareInch => "in2",
+			SquareFoot => "ft2",
+			SquareYard => "yd2",
+			SquareMile => "mi2",
+			Are => "a",
+			Decare => "daa",
+			Hectare => "ha",
+			Acre => "acre",
+			_ => right.unit.singular(),
+		};
+		let display = format!("{}/{}", cur_upper, denom_abbrev);
+		let key = format!("{cur_lower}_per_{denom_abbrev}");
+		let composite = crate::extra_units::upsert_unit(
+			&key,
+			&display,
+			&display,
+			CurrencyPerArea,
+			left.unit.weight() / right.unit.weight(),
+		);
+		Ok(Number::new(left.value / right.value, composite))
+	} else if lcat == Mass && rcat == Volume {
+		// 5 g / 64 floz => g/floz (convertible to g/ml, kg/l, etc)
+		let mass_abbrev: &str = match left.unit {
+			Milligram => "mg",
+			Gram => "g",
+			Hectogram => "hg",
+			Kilogram => "kg",
+			MetricTon => "t",
+			Ounce => "oz",
+			Pound => "lb",
+			Stone => "st",
+			ShortTon => "ston",
+			LongTon => "lton",
+			_ => left.unit.singular(),
+		};
+		let vol_abbrev: &str = match right.unit {
+			Milliliter => "ml",
+			Centiliter => "cl",
+			Deciliter => "dl",
+			Liter => "l",
+			Teaspoon => "tsp",
+			Tablespoon => "tbsp",
+			FluidOunce => "floz",
+			Cup => "cup",
+			Pint => "pt",
+			Quart => "qt",
+			Gallon => "gal",
+			OilBarrel => "bbl",
+			_ => right.unit.singular(),
+		};
+		let display = format!("{}/{}", mass_abbrev, vol_abbrev);
+		let key = format!("{mass_abbrev}_per_{vol_abbrev}");
+		let composite = crate::extra_units::upsert_unit(
+			&key,
+			&display,
+			&display,
+			MassPerVolume,
+			left.unit.weight() / right.unit.weight(),
+		);
+		Ok(Number::new(left.value / right.value, composite))
+	} else if lcat == Volume && rcat == Mass {
+		// ml/g etc
+		let vol_abbrev: &str = match left.unit {
+			Milliliter => "ml",
+			Centiliter => "cl",
+			Deciliter => "dl",
+			Liter => "l",
+			Teaspoon => "tsp",
+			Tablespoon => "tbsp",
+			FluidOunce => "floz",
+			Cup => "cup",
+			Pint => "pt",
+			Quart => "qt",
+			Gallon => "gal",
+			OilBarrel => "bbl",
+			_ => left.unit.singular(),
+		};
+		let mass_abbrev: &str = match right.unit {
+			Milligram => "mg",
+			Gram => "g",
+			Hectogram => "hg",
+			Kilogram => "kg",
+			MetricTon => "t",
+			Ounce => "oz",
+			Pound => "lb",
+			Stone => "st",
+			ShortTon => "ston",
+			LongTon => "lton",
+			_ => right.unit.singular(),
+		};
+		let display = format!("{}/{}", vol_abbrev, mass_abbrev);
+		let key = format!("{vol_abbrev}_per_{mass_abbrev}");
+		let composite = crate::extra_units::upsert_unit(
+			&key,
+			&display,
+			&display,
+			VolumePerMass,
+			left.unit.weight() / right.unit.weight(),
+		);
+		Ok(Number::new(left.value / right.value, composite))
 	} else if lcat == Power && rcat == ElectricCurrent {
 		// 1 watt / 1 ampere = 1 volt
 		let result = (left.value * left.unit.weight()) / (right.value * right.unit.weight());