Abstract: A fuel-lubricating oil proportioning and mixing device for mixing an appropriate quantity of lubricating oil with an appropriate quantity of fuel in the fuel tank of an internal combustion engine, principally for motor boats powered by two-cycle engines. The device of the invention comprises a lubricating oil reservoir separate from the fuel tank and a graduated measuring container connected to the oil reservoir through a solenoid actuated two-position valve and a reversible pump. The oil measuring container is connected to the fuel tank filler through the pump, the valve and a discharge line. After a known quantity of fuel has been taken in the fuel tank, the pump is actuated to draw from the oil reservoir through the valve an appropriate proportional quantity of oil into the measuring container.