Carbon-dioxide production and hydrocarbon degradation of refined petroleum hydrocarbon in soils treated with 5% gasoline, kerosene and diesel oil were investigated. Soil for study was bulked from around acar park in Port Harcourt. Soil samples were collected at weekly intervals for four weeks and subsequently at monthly intervals for four months, between the months of March and July 1998. The volume of carbon-dioxide produced in 40g soil ranged from 17.6 mg to 105.6mg for the control soil and from 30.8mg to 154mg for the hydrocarbon-contaminated soils. Statistical analysis using paired t- test between control and hydrocarbon – contaminated soils showed significant differences for gasoline – contaminated soils. The rate of hydrocarbondegradation ranged from 0 ìgg-1 oil h-1 to 0.60 ìgg-1 oil h-1 for the control soil; 0.05 ìgg-1 gasoline h-1 to 1.67 ìgg-1 gasoline h-1 and from 0.12 ìgg-1 diesel oil h-1 to 1.31 ìgg-1 diesel oil h-1 for the hydrocarbon contaminated soils respectively. Carbondioxide production was generally higher in the hydrocarbon – contaminated soils than in the control soil with gasoline> diesel oil > control soils.