This paper is devoted to analytical modelling of so-called pumping kite generator whose operating principle is to mechanically drive a groundbased electric generator using tethered kites. The refined crosswind motion law is derived in the case of equilibrium motion of the kite. The paper also presents the theory of a gently sloping kiteline. The main purpose of the study was to estimate the mechanical energy output of the pumping kite wind generator. A simple approximate formula for the mean mechanical power generated by the deploying kite is obtained. (c) 2008 Elsevier Ltd. All rights reserved.