Mean Machine have suffered their first defeat of the season as they went down 19-12 to USIU in the ninth round of the Championship.
Aggrey Obina, Tobias Otieno and Junior Onyango crossed over for USIU with Onyango and Eliud Mulakoli adding the extras for their fifth win of the season.
Machine had gone for seven matches without a draw or loss and now Oilers remain the only unbeaten side.
For the win, USIU stays fifth with 22 points due to Catholic’s win over South Coast Pirates. Machine, who were top going to the match day, drop to second with 34 points. Oilers move to the top of the table with 37 points after beating Egerton Wasps 19-8.
Monks beat Pirates 21-10 with tries from Louis Boyi, Teddy Owino and Max Omondi to gain revenge over a side that beat them 31-24 in the first round.