Oligomerization of olefins

A process for oligomerizing olefins, comprising:

• passing a hydrocarbon feedstock mixture containing olefins of from 2 to 8 carbon atoms over a molecular sieve having a pore diameter of from greater than 4 angstroms to 15 angstroms, thereby removing catalyst poisons from the feedstock mixture;
• removing polyunsaturated hydrocarbons from the hydrocarbon feedstock mixture by selective hydrogenation either before or after passage of the hydrocarbon feedstock mixture over the molecular sieve;
• and then
• oligomerizing said olefins by passing the hydrocarbon feedstock over a nickel-containing catalyst at a temperature of from 0.degree. to 200.degree. C. and at a pressure of from 1 to 70 bar absolute.