DETROIT ( TheStreet) -- When the Sonic is introduced in the fall of 2011, it will become the only sub-compact made in the U.S. But it will face tough competition from the sub-compacts already in the market, whether they are U.S.-built or not. Sub-compacts cars today account for about 3.5% of the industry, but GM ( GM) thinks it will grow to 4.5% in the next two years, with the potential to increase further if fuel prices rise. GM spokeswoman Margaret Brooks said the competition in the sub-compact market is one of the factors that led the automaker to decide to build the Sonic. "Once you see a critical mass of market opportunity, it made sense to look at doing the manufacturing in the U.S," she said. GM has not announced pricing, but Brooks said the car will be competitive with Fiesta, which starts at $13,320, and Fit, which starts at $15,100. The Sonic will not be a bare-bones subcompact, but rather it will be roomy and will have advanced safety features. It will get about 40 miles per gallon. TrueCar.com analyst Jesse Toprak noted that "We've seen the sub-compact segment become almost fashionable" because it now includes desirable cars, along with a predilection to buy them. Here's a look at three other major players already in this growing market.