Cruze sold 21,807 units in August, making it the fifth best-selling vehicle in the U.S. as well as the best-selling compact car -- for the fourth month in a row. Cruze sales also exceeded 20,000 units for the fifth consecutive months. Year-to-date, it has sold 169,427 units. The sustained demand means that Chevrolet dealers have only about a 30-day supply, about half the industry average. GM is going to further test its luck in small car segment, when the sub-compact Sonic begins to arrive at dealers this month.