This study addresses the issue of refueling emissions from gasoline vehicles by developing an unsteady multivariate predictive model that accounts for variations in pressure and temperature within the fuel tank. The effectiveness of the model was validated through experimental testing. The findings indicate that increases in the fuel tank temperature, dispensed fuel temperature, and Reid vapor pressure led to a significant increase in refueling emissions, with the fuel tank temperature having the most notable impact - a 32% increase in emissions when the temperature increased from 293 K to 303 K. The installation of an Onboard Refueling Vapor Recovery (ORVR) system can substantially decrease refueling emissions by over 96% with the addition of an isolation valve, further reducing the emissions by approximately 3.42%. Prolonging the opening of the fuel tank cap before refueling and higher ambient temperatures both contributed to increased evaporative emissions, suggesting that the use of a mechanical check valve to seal the refueling port could minimize emissions during refueling wait times. Increments in the refueling rate slightly reduced emissions, although the effect was marginal when turbulence diffusion was not considered.