In a large bowl, measure out the butter and peanut butter. Microwave in 30-second intervals until completely melted and smooth; should take about 1 1/2 minutes.
Stir in powdered sugar and rice Krispies and gently incorporate until fully mixed together.
Using a 2 teaspoon cookie scoop, scoop mixture into 24 even balls. Roll in between palms to smooth completely. Place onto a parchment (or wax) paper-lined baking sheet. Freeze 10 minutes.
While peanut butter balls are freezing, melt chocolate and vegetable oil together in a small microwave-safe bowl. Microwave in 30-second intervals until completely melted and smooth.
Drop the frozen balls one at a time into the melted chocolate. Use a fork to roll ball evenly in chocolate. Lift ball out of the chocolate with the prongs of the fork and tap gently to remove any excess chocolate. Place back on parchment paper.
Continue coating balls in chocolate until they are all coated. Chill until chocolate hardens. Serve.