A process is disclosed for producing a compound of the formula: CF.sub.3 CHXCF.sub.3-z Y.sub.2 where X and Y are independently selected from the group consisting of H and Cl, and z is 0 or 1. The process involves (1) contacting CCl.sub.3 CHXCC.sub.3-z Y.sub.z,CCl.sub.2-z .dbd.CXCC.sub.3, and/or CCl.sub.2 CX.dbd.CC.sub.3-z Y.sub.z starting material, with hydrogen fluoride at a temperature of less than 200.degree. C. to produce a fluorination product of said starting material which includes at least 90 mole percent total of C.sub.3 HXY.sub.z Cl.sub.6-z-x F.sub.x saturated compounds and C.sub.3 XY.sub.z Cl.sub.5-z-y F.sub.y olefinic compounds, wherein x is an integer from 1 to 6-z and y is an integer from 1 to 5-z, (the fluorination product including no more than about 40 mole percent of the desired product, CF.sub.3 CHXCF.sub.3-z Y.sub.z); (2) contacting saturated compounds and olefinic compounds produced in (1) with hydrogen fluoride in the vapor phase at a temperature of from 200.degree. C. to about 400.degree. C. in the presence of a fluorination catalyst; and (3) reacting a sufficient amount of said compounds, wherein x is an integer from 1 to 5-z and olefinic compounds produced in (1) with hydrogen fluoride in the vapor phase at a temperature of from 200.degree. C. to about 400.degree. C. in the presence of a vapor phase fluorination catalyst to provide an overall selectivity to CF.sub.3 CHXCF.sub.3-z Y.sub.z of at least about 90 percent based upon the amount of starting material reacted with HF in (1) and (2).