Mexico's car and light-truck sales fell 19.6 percent in November from a year earlier to 78,544 vehicles.
In the first 11 months of the year, sales slid 5.1 percent to 924,188.
Through July, Mexico's sales were almost even with 2007 levels. But since then sales have spiraled downward at an increasing pace.
Sales dropped 4.8 percent in August, 10.7 percent in September and 14.3 percent in October.
In November, car sales fell 18.2 percent to 44,020.
Truck sales fell 21.3 percent to 34,524.
Nissan Motor Co. and General Motors continue to alternate as Mexico's market leader.
In November, Nissan came out on top. Its sales slipped 11.3 percent to 16,100. GM's sales tumbled 23.8 percent to 14,971.
For the first 11 months, Nissan holds a thin 45-vehicle edge. Nissan's sales are up 1.6 percent to 192,014, and GM's are down 5.8 percent to 191,969.
Among other automakers, Ford Motor Co.'s November sales fell 19.4 percent to 11,077, and Volkswagen AG's sales dropped 18.0 percent to 10,783. Chrysler LLC's sales fell 22.5 percent to 9,134.