New Delhi, March 5 -- Shares of Indraprastha Gas Ltd (IGL) and Mahanagar Gas Ltd (MGL) have slipped 7% and 10%, respectively, in the first three trading days of this week, after the US and Israel attacked Iran over the weekend.

Both city gas distribution (CGD) companies derive almost three-fourth of their sales volume from compressed natural gas (CNG) that competes with other auto fuels (petrol and diesel).

Even if auto fuels are priced similarly to CNG, the latter still offers the advantage of being relatively clean and more efficient, with 15-20% higher mileage. But things could change due to the Iran conflict. Global crude oil and natural gas prices have now spiked, lifting prices of auto fuels and CNG.

However, the threat to CNG pr...