An oar is a tool used for marine propulsion . Oars have a flat blade at one end. The oarsmen grasp the oar at the other end. What distinguishes oars from paddles is that paddles are held by the paddler, and are not connected with the vessel. Oars generally are fastened to the vessel.

Oarsmen generally face the stern of the vessel, reach as far as they can towards the stern, insert the blade of their oar in the water. As they lean back, towards the vessel's bow, the blade of their oars sweeps the water towards the stern, providing forward thrust.

For thousands of years vessels were powered either by sails, or the mechanical work of oarsmen, or paddlers. Some ancient vessels were propelled by either oars or sail, depending on the speed and direction of the wind.

Oars used for transportation

The oars used for transportation come in a variety of sizes. The oars used in small dinghies or rafts can be less than 2 metres long. In classical times warships were propelled by very long oars that might have several oarsmen per oar. These oars could be more than a dozen meters long.

Oars used for competitive rowing

The oars used in competitive rowing are long (250-300 cm) poles with one flat end about 50 cm long and 25 cm wide, called the blade. The part of the oar the oarsman holds while rowing is called the handle . While rowing, the oars are supported by metal frames attached to the side of the boat called outriggers.

Classic oars were made out of wood, but modern oars are made from synthetic material, the most common being glassfiber. Since the use of synthetic materials, the weight of an oar has come down from over 7 kg, to less than 2.5 kg. Commonly, the large paddles used in coxed and coxless pairs, fours, and eights are called oars, while the smallers ones used in the single, double, and quadruple sculls are called sculls.

The most commonly used brands of oars are Empacher, Dreissigacker, and Croker .