In a food processor, crush the Oreo cookies into fine crumbs.
In a mixing bowl, combine the crushed Oreos with the softened cream cheese. Mix until well combined and smooth.
Use your hands to form the mixture into small balls, about 1 inch in diameter, and place them on a baking sheet lined with parchment paper.
Freeze the balls for about 30 minutes, or until firm.
While the truffles are chilling, melt the chocolate chips in a microwave-safe bowl in 30-second intervals, stirring in between until smooth. If desired, stir in the vegetable oil to thin the chocolate.
Dip each chilled Oreo ball into the melted chocolate, using a fork to coat evenly. Allow excess chocolate to drip off before placing them back on the parchment-lined baking sheet.
If desired, sprinkle with crushed Oreos or sprinkles before the chocolate sets.
Refrigerate the truffles for at least 30 minutes to allow the chocolate to harden.