Oil sand exploitation is enhanced, by using a downhole apparatus comprising a casing (130) for housing a water conduit for receiving water via a water pipe, at least one steam generation chamber mounted to the peripheral surface of the casing and being in fluid communication with said water conduit and having at least one steam outlet, at least one electrical heater, being thermally connected to said steam generation chamber, if the downhole apparatus further comprises at least one crude oil conduit (125) for recovering crude oil, which has been mobilized by said steam.