A method may comprise, on board a vehicle and executed by a vehicle controller, determining a liquid volume based on a fuel level sensor, determining a gas volume based on the liquid volume, the liquid volume comprising first and second fuels, the gas volume comprising the second fuel, determining a second fuel solubility in the first fuel based on a fuel temperature sensor, determining first and second fuel quantities based on the second fuel solubility, and adjusting engine operation based on the first and second fuel quantities.