Overseas BMW and Mercedes Benz sell a range of powerful yet fuel-efficient four-cylinder petrol and diesel models, but here in the U.S. both carmakers only offer six-cylinder engines and above. With tougher fuel-economy and emissions regulations set to roll in, however, both carmakers are now rethinking their stance against selling four-cylinder models in the U.S. luxury market.

BMW and Mercedes have previously expressed a desire to bring four-cylinder cars to the U.S., especially considering the effect that impending fuel economy standards will have on their fleets but neither carmaker has made any moves yet.

For both, the move is taking them into uncharted territory - the last time BMW tried to sell a four-cylinder car in the U.S. was back in 1999 with the poor-selling 318ti hatchback, while Mercedes' last effort in that area was around 5 years ago with its C-Class and SLK convertible.

Speaking with Automotive News, BMW’s U.S. chief Jim O'Donnell said the company is considering a new twin-turbocharged four-cylinder petrol engine with direct-injection technology for the 1 and 3-series models and upcoming X1 and next-generation X3 crossovers. The new engine family will have as much power as BMW’s current six-cylinder range but with better fuel-economy and lower emissions.

The advanced engines, however, cost more to manufacture than the current six-cylinder units and this premium would likely be passed on to consumers. According to O'Donnell, BMW is waiting to see what outcome on fuel-economy standards is determined by the U.S. government before it makes its decision.

Mercedes, on the other hand, is considering bringing a new 2.2L four-cylinder diesel for the E-Class, C-Class and GLK onto the market. The new engine, which develops 204hp (150kW) and returns fuel-economy of 40mpg (5.88L/100km) on the highway, has already been previewed in last month’s E250 Bluetec concept. Like BMW, Mercedes is also yet to make a decision on the issue.