Oil spill is the accidental release of petroleum products into the environment. Oil spill is a form of pollution that includes releases of crude oil from tankers, offshore platforms, drilling rigs and wells, as well as spills of refined petroleum products (like gasoline, diesel) and their by-products, and heavier fuels used by large ships such as bunker fuel, or the spill of any oily refuse or waste oil.
Oil spills in the ocean may result in oil pollution over large areas and present serious environmental hazards. The primary source of accidental oil input into seas is associated with oil transportation by tanker ships and underwater pipelines.
During the period of 1990 and 1999, an average of 150,000 tons of oil spilled each year into the world's oceans and waterways.
Oil spills affect water in a variety of ways. When oil is released into water, it does not blend with the water. Oil floats on the surface of salt and fresh water. Over a very short period of time, the oil spreads out into a very thin layer across the surface of the water. This layer, called a slick, expands until the oil layer is extremely thin. This layer is called a sheen and is usually less than 0.01 mm thick.
Oil spills on the surface of the water are subjected to the whims of weather, waves and currents. All these natural forces move slicks across the surface of the water. In addition, these forces stir up the oil slick and also control the direction the slick moves in. An oil spill far out at sea can be carried ashore by wave and current action. Rough seas can split an oil slick apart, carrying some oil in one direction and more in another. In contrast, a near shore oil spill can be totally controlled by currents and wave action that causes the oil to come ashore, damaging marine shoreline habitat.
Different types of oil react differently when spilled. Some evaporate in small amounts while others break down quicker. After the sheen breaks down, a moderate amount of oil will break down and be deposited on the bottom of the ocean. This usually happens in shallow water. Certain types of microbes will break apart and consume the oil, but this in no way makes up for the damage done during the spill. In addition, when oil breaks apart and sinks to the ocean floor, it contaminates the underwater habitat too.
The most visual part of an oil spill is the harsh effects oil has on the coastline. Pictures of oil covered birds and sea mammals are common. Oil is thick and sticks to everything it touches. While the most visual part of the damage might be the birds and wildlife we see on TV, consider that the oil covers everything right down to a grain of sand. Every rock, every piece of driftwood, saw grass, sand, soil and every microscopic habitat is destroyed or affected by the thick oil that washes ashore after a spill. Oil spills affect the coastal habitat from the smallest shells up to the largest boulders.
Unless there is a concerted effort to clean the shoreline, oil will basically stay on shore until weather and time break the oil down. The process is extremely slow which is why so many environmentalists work diligently to clean beach areas, rocks, and shoreline that have been contaminated. The gooey mass that makes up an oil slick litters the shoreline with ugly black tar. What makes it so very dangerous is that the coastline is where so much marine life is concentrated. Typically, shore areas are the nurseries for fish and marine life, in addition to being the home of many young marine mammals. Contaminated shorelines are not only unsightly, but also extremely dangerous to any wildlife in the area
 Marine Life and Wildlife
When oil floats on the water surface,marine mammal surfaces in the center of a slick and ingests the oil. If this marine mammal is miles from the oil spill but happens to ingest a fish that swam through it, he is poisoned. The effects are far reaching. Marine and coastal life can be contaminated in a number of way, through poison by ingestion, destruction of habitat and direct contact with oil.
Ingesting oil can cause any number of problems. Death is the obvious one. However, if an animal ingests oil-saturated food, the effects might be longer reaching that simply making the animal ill. People are not aware of the immediate impact to an animal's ability to mate and have viable offspring after being exposed to oil contamination. Fish ingest oil suspended in the water through their gills. It is known that this affects their ability to reproduce.
Habitat destruction is all too obvious with an oil spill. The most visible would be seen on shore but beneath the water, there is a very delicate balance in the reefs and shallow water habitats. Plankton, the smallest organisms, are affected by oil spills. This effect moves right on up the food chain. Of particular concern are the very delicate sea life, such as clams and mussels that feed on plankton.
Direct contact with oil harms any animal that comes in contact with the oil. Bird's feathers are designed to repel water to protect the animal from the elements, in addition to allowing many birds to float on the water when resting or searching for food. When oil cakes the feathers of a bird, it keeps the feather from repelling water. Oil also weighs down the bird, keeping it from flying. If a bird isn't cleaned of the oil, it's a sure license to death. Many birds ingest deadly amounts of oil trying to clean their feathers. The same holds true for marine mammals. Marine mammal fur acts as an insulator to keep the animal warm in the coldest waters. When oil saturates the fur, it ruins the ability of the fur to retain heat. Again, marine mammals can ingest the oil when trying to clean their fur.
 Clean up method
- Containment and skimming - buoyant booms which float on the water and a skirt that hangs just below the water, keeps and contain the slick and oil from spreading further. This makes it easier to skim and collect the oil from the surface, using boats that suck or scoop the oil from the water and into containment tanks.
- Controlled burning - where oil is on fire, but this produces toxic smoke, and is not recommended to be used in a spill near coastal settlements.
- Dispersants - are chemicals that acts like detergent that breaks down oil more quickly than natural elements alone. Dispersants break the oil slick apart, allowing oil droplets to mix with water and be absorbed into the aquatic system more quickly. Unfortunately, these chemicals pose their own danger as broken-down oil can be absorbed by marine life and may enter into the food chain.