Clearing-up the confusion over the issue, the Union ministry of surface transport has said companies can convert buses of all models which have an engine capacity of more than 1,301 cc. The ministry clarified the matter in a reply to a letter by the Delhi transport department. The clarification was sought in the wake of a controversy over whether a conversion company was allowed to convert all models of diesel-run buses to CNG mode, or if it could convert only thosse for which it had approval.