Oil has broken through the landmark $100 a barrel, driven by a slumping dollar, geopolitical instability and worries over a winter fuel supply crunch.

See how the price of oil has risen - and fallen - since 1970 against a background of key world events.

1973 ARAB-ISRAELI WAR

Alarmed by Israeli successes, the Organisation of Petroleum Exporting Countries (Opec) orchestrated the Arab oil embargo, sending prices soaring by 400% in six months.

It was the first time oil had been used as a political weapon, putting pressure on the US which, in turn, persuaded Israel to accept UN mediation on the crisis.

1979 IRANIAN REVOLUTION

Months of turmoil in Iran led to the exile of the Shah and the declaration of an Islamic republic.

It also led to a reduction in oil production and, at one point, the flow of crude oil from Iran was almost halted. Nervousness about the stability of Iran brought together the other major Arab oil-producing states to ensure supply and increase prices.

1980 IRAN-IRAQ WAR

Iran weakened by the revolution was invaded by Iraq in September 1980. By November, the combined oil production of the two countries was only one million barrels a day, 6.5m fewer barrels than the year before.

It meant a worldwide reduction in crude oil production of 10%. The combination of the Iranian revolution and the Iran-Iraq war caused crude oil prices to more than double from $14 in 1978 to $35 in 1981.

1986 OIL PRICE CRASH

Higher oil prices led to a reduction in demand as consumers and industry looked at ways of becoming more energy-efficient.

The price rise also led to increased exploration for new sources of oil outside the traditional oil-producing regions.

Saudi Arabia suffered from the reduction in revenue, made worse by new Opec quotas which meant it had also been forced to reduce production.

It responded by increasing production in early 1986.

Crude oil prices plummeted below $10 per barrel - but the Saudi revenue remained about the same.

1990 GULF WAR

Iraq wanted to gain control of the world's third largest oil producer to give it more control over the world market.

Following the Gulf war to liberate Kuwait, crude oil prices entered a period of steady decline, reaching their lowest level in 1994 for 21 years.

1997 ASIAN FINANCIAL CRISIS

The rapid growth in Asian economies came to a halt leading to lower consumption of oil - just at a time when Opec had begun increasing production.

The combination sent prices plummeting, through to December 1998.

2001 9/11

Oil prices suffered a downturn as Russian oil production increased, and the US economy went into decline.

Opec tried to stem the reduction by cutting production - but the terror attacks on 11 September sent oil prices plummeting again.

Prices were down by about 35% by the middle of November. Opec delayed cutting production again until early 2002, when prices began to move upwards once more.

2003 IRAQ WAR

The American-led invasion of Iraq led to the loss of oil production in the Gulf state. In mid- 2002, there were over six million barrels per day of excess production capacity and by mid 2003, this had dropped to below two million.

It dropped still further in 2004-5. A million barrels per day is not enough spare capacity to cover for any sudden drop in production and it led to an increase in prices.

2006 LEBANON CONFLICT

Although neither Israel nor Lebanon are oil producers, the conflict increased tension in the Middle East sending prices soaring.

2008 $100 BARREL

Geopolitical tension in Kenya, Algeria and Pakistan, as well as the threat of US sanctions against Iran have played their part.

At the same time, there are fears of a cold winter in the US and Europe, and increased demand from China and India as well as the US.

The falling US dollar has also driven up oil prices as they have to gain to compensate for a slide in the currency.