Preheat the oven to 350°F and grease and line an 8×12 or 9×11 baking pan with parchment paper.
In a large bowl, combine the melted butter, oil, granulated sugar, and brown sugar. Whisk until well combined.
Add vanilla and eggs, beating for 30 seconds until the batter lightens.
Sift in flour, cocoa powder, and salt. Mix until just combined.
Gently fold in the chocolate chips.
Pour half of the batter into the prepared pan, spread evenly, layer on the Oreos, and top with the remaining batter.
Bake for 25–30 minutes or until the center no longer jiggles. Do not overbake for fudgy brownies.
Once cooled, make the frosting.