The lifetime of wireless sensor networks can be improved by introducing mobile sinks. A data collection method is proposed in order to support hybrid sink mode in wireless sensor networks where static and mobile sinks coexist. One or more mobile sinks cooperate with the static sink(s). These mobile sinks broadcast status update periodically to only a subset of adjacent nodes. Sensor nodes send or forward data packets to the sink which is the nearest in hop counts. The correct data transmission between the mobile sinks and the last hop sensor node is guaranteed by using ACK-RETRANSMIT method. Using this method

the network lifetime improves with the increase of the number of mobile sinks. Simulation study shows that more than 600% lifetime improvement achieves when the ratio of the mobile sinks to the sensor nodes is above 7.5%. When the load of network is high

the maximum success rate of data transmission achieves 91%

which is 8.3 times compared to the network with only one static sink. Meanwhile

data transmission delay remains at a low level.