A positive displacement rotary system may include a main rotor and a slotted rotor. The main rotor can include an interior cavity and a fixed vane (or blade) that is attached to the peripheral and side walls of that cavity. The slotted rotor is positioned within the main rotor interior and includes a slot for the main rotor blade. The main and slotted rotors rotate about parallel axes that are offset from one another. As the rotors turn, separate chambers are formed between the blade and an inter-rotor seal, with the inter-rotor seal located at or near a rolling contact between the outer surface of the slotted rotor and an inner perimeter wall of the main rotor cavity. The separate chambers contract and expand as the rotors rotate.