Essar Oil Ltd on Tuesday announced the successful commissioning of a diesel hydro-treater unit I (DHDT-I) at its refinery at Vadinar in Jamnagar district of Gujarat. With the phase-wise commissioning of three additional units slated for the end of this month, the refinery is now on track to complete the Phase I expansion by March 2012, which entails addition of nine new units that would expand capacity to 18 million tonnes a year, the company said.