A series of SAE 5W-30 and SAE 10W-30 engine oils was evaluated in a New York City taxi fleet to study the performance of prototype API SG engine oils. Key formulation variables studied were SAE viscosity grade and Viscosity Index improver chemistry. A good correlation was established between Sequence VE sludge and varnish results and field performance. The deposit control value of dispersant Viscosity Index improvers was demonstrated. Formulations based on polymethacrylate Viscosity Index improvers performed directionally better in the field than the Sequence VE results predicted. Overall, the field performance of API SG quality oils was excellent.