An engine for converting thermal energy to kinetic energy is provided. The engine includes a body of fluid having a first zone and a second zone, a thermal energy source thermally connected to the first zone for providing thermal energy thereto, and a thermal energy sink thermally connected to the second zone for removing thermal energy therefrom such that the first zone has a temperature greater than the second zone. The engine further includes a movable loop, which extends between the first zone and the second zone, and a plurality of containers which are positioned in the body of fluid and attached to the loop such that the loop and the containers move conjointly between the first zone and the second zone. Each of the containers expands to a first volume when it is in one of the first and second zones, and contracts to a second volume when it is in the other one of the first and second zones. A working fluid is provided in each of the said containers to cause the containers and the loop to move between the first and second zones.