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We present an analysis of the registration component of a proposed image guidance system for image guided liver surgery, using contrast enhanced CT. The analysis is performed on a visually realistic liver phantom and in-vivo porcine data. A robust registration process that can be deployed clinically is a key component of any image guided surgery system. It is also essential that the accuracy of the registration can be quantified and communicated to the surgeon. We summarise the proposed guidance system and discuss its clinical feasibility. The registration combines an intuitive manual alignment stage, surface reconstruction from a tracked stereo laparoscope and a rigid iterative closest point registration to register the intra-operative liver surface to the liver surface derived from CT. Testing of the system on a liver phantom shows that subsurface landmarks can be localised to an accuracy of 2.9 mm RMS. Testing during five porcine liver surgeries demonstrated that registration can be performed during surgery, with an error of less than 10 mm RMS for multiple surface landmarks.