A system and method for in situ upgrading of crude oil is provided. The system includes at least one injection well, at least two first production wells, and at least one second production well. The at least one injection well has a vertical portion and a plurality of non-vertical portions connected to the vertical portion. The at least two first production wells are preferably equi-spaced and each has a horizontal portion with a first axial direction, wherein each said horizontal portion of the first production wells is horizontally spaced apart. The at least one second production well has a horizontal portion with a second axial direction. The catalytic reactor is placed at the horizontal portion of the at least one second production well such that oil coming through the second production well will first go through the catalytic reactor for hydroprocessing.