State-run oil marketing companies (OMCs) have not changed petrol and diesel prices for a week now while crude oil touched $50 a barrel last week, a first since March. The rise in crude oil prices may dent marketing margins if not passed on, however, some say OMCs may have a cushion to absorb. On Monday, petrol price in Mumbai was at Rs 90.34 per litre, while diesel sold at Rs 80.51 per litre, according to the Petroleum Planning and Analysis Cell (PPAC). Both have been at the same price since December 7. In the global market, Brent crude oil prices last week touched $50 per barrel for the first time since March.