Several routing protocols have been proposed for mobile Wireless Sensor Networks. Some are based on variants of flooding algorithms leading to redundant copies of message unnecessarily. Despite various optimizations, such routing methods still remain inefficient. This paper deals with region-based routing which has been introduced to reduce the number of messages in the network. We propose an energy efficient routing algorithm, called Ellipse-Routing, which is based on Region-based Routing. A virtual ellipse is built thanks to source and destination positions. So, only nodes within this region forward a message. For a given energy consumption model, we select a suitable ellipse factor and a transmission range, leading to a delivery rate close to 100\% while minimizing energy consumption. Then, we extend the proposed scheme to take into account position errors. Performances of roposed algorithms are shown thanks to simulations.