A process for preparing a polyolefin, including polymerizing olefins in the presence of an antistatic agent made from or containing an alkylene oxide derived polymer made from or containing in average from about 10 to about 200 repeating units —(CH2—CHR—O)— with R being hydrogen or an alkyl group having from 1 to 6 carbon atoms, wherein the alkylene oxide derived polymer is a random copolymer of ethylene oxide and other alkylene oxides and a ratio of n:m is in the range of from 6:1 to 1:1, wherein (n) is the average number of repeating units —(CH2—CH2—O)— derived from ethylene oxide and (m) is the average number of repeating units —(CH2—CHR′—O)— derived from the other alkylene oxides with R′ being an alkyl group having from 1 to 6 carbon atoms, and the end groups of the alkylene oxide derived polymer are —OH groups.