Vegetable Oil (Best Option)
Use 7/8 cup vegetable oil per 1 cup butterVegetable oil is a pure fat, similar to butter but without the milk solids and water. This allows it to keep the crumb moist and tender, which is crucial for red velvet cake's characteristic texture. The oil's neutral flavor ensures the cocoa and buttermilk notes remain prominent.
For best results, use a neutral oil like canola or sunflower oil. Avoid strongly flavored oils. Since oil is liquid at room temperature, the batter may be slightly looser; do not overmix to prevent a dense cake.
Compared to butter, the cake will be slightly less rich and may lack the subtle buttery flavor, but the texture and moisture will be very close to the original, making it the best single substitute.