PURPOSE: To provide the new allophonate esters useful as cleaning agents for gasoline engines especially as agents to prevent depositions on gasoline intake valves or in a fuel chamber.

CONSTITUTION: Alophanate esters of formula I [R is 9-25C alkyl; R1 is 2-4C oxyalkylene; (m) is 0 or 1; (n) is 5 to 30], e.g. Nnonylphenoxypolyoxypropylene amine of 2-hydorxy-ethane as shown by the formula II. The compounds of formula I are obtained by allowing polyether amines of formula III to react with urea and ethylene carbonate. The compounds of formula I are functional in preventing and removing the depositions on intake valves and in the results lower the necessity of enhancing octane value of gasoline and effective in decreasing the amount of NO. emission. An effective amount of the compounds of the formula I is added to a main ingredients of hydrocarbon fuels having b.p. within the range of gasoline's b.p., thereby obtaining the motor fuel compositions.