A gas pressure booster and a method for using it, which recovers fugitive gas emissions such as at atmospheric pressure, boosts them such as to the pressure level of the low pressure gas sink, and returns them to, e.g., the low pressure gas sink, in a single stage of compression. No electricity or cooling water is required. All gas used to drive the vapor recovery booster may be recovered and vented to the low pressure gas sink.In one preferred embodiment, the gas pressure booster includes a drive cylinder and a boost cylinder interconnected by reciprocating drive and boost pistons. The drive piston supplies force powered by a first gas stream within the drive cylinder which exhausts to a second gas stream at a lower pressure. Fugitive gas emissions may be captured and transported to the lower pressure second gas stream to eliminate gas discharged to atmosphere. The need for boosting a gas multiple ratios is eliminated, as the pressure of the fugitive emission vapor is equalized to the low pressure gas sink at the end of the piston suction stroke. Preferably, a four-way valve operating on differential gas pressure may be used to automatically actuate the reciprocating piston.