Mobile soft robots show great potential for exploration of unknown and hard to navigate environments. Sadly, most of these robots are currently being held back by their power sources and control systems. These components, which are usually quite heavy and bulky, need to be integrated before mobile soft robots can cut their tethers and explore the world autonomously. Soft robots should be mindful of their energy consumption to minimize the requirements on the power supply. However, the efficiency of their actuators is still a not well understood area of research. We attempt to pave the road for future research into this subject by developing a testing protocol based on a simplified analytical model. We built an experimental setup and investigated the efficiency of soft pneumatic extension actuators. We found that actuator designs which reduce axial stiffness produced higher efficiency. Additionally, we found that efficiency increases with load, until it is limited by the buckling load. Unfortunately, these two conditions seem to conflict with each other since a lower axial stiffness also reduced the buckling load. Future actuator designs should therefore try to combine a low axial stiffness with high load bearing capabilities. Also, this research should be extended to different classes of soft actuators as well as investigating non-ideal circumstances. We believe this research aids in the general understanding of efficiency of soft actuators and act as a stepping stone for future research.