Combine buttermilk, oats, and vanilla; let mixture stand for 10 minutes, stirring occasionally. Stir in oil and egg.
Combine flour, brown sugar, baking soda, and salt in a large bowl. Add oat mixture to flour mixture, stirring until smooth.
Spoon 1/3 cup of batter onto a hot, nonstick griddle or nonstick skillet. Turn pancakes when tops are covered with bubbles and edges look cooked.
Serve at once with butter and maple syrup.