FACTBOX: Why oil prices hit a record high above $145

(Reuters) - U.S. crude oil on Thursday hit an all-time high above $145 a barrel.

Prices have rallied from a dip below $50 at the start of 2007 and this year have risen by around 50 percent from $95.98 a barrel at the end of last year.

Adjusted for inflation, oil is well above the $101.70 peak hit in April 1980, according to the International Energy Agency, a year after the Iranian revolution.

The balance of demand and supply is tight with daily demand of roughly 86 million barrels per day, almost the same level as daily supply.

The following are other major factors that have driven the oil market higher.

DOLLAR WEAKNESS AND FUNDS

A combination of weaker performance in other asset classes and expectations of continued strength across the commodities complex has drawn in investors and speculative funds, providing further support for the market.

An added incentive for them has been the weakness of the dollar against other major currencies, which makes dollar-denominated commodities relatively cheap.

They are also seeking an inflation hedge, as commodities tend to rise when other asset classes fall.

OPEC

The Organization of the Petroleum Exporting Countries (OPEC) has been at the forefront of those citing speculation and a weak dollar as the reason for higher prices, saying it is pumping enough oil to keep the market balanced.

Saudi Arabia, the biggest OPEC producer, has said it will raise output to 9.7 million barrels per day (bpd) in July up from around 9.1 million bpd in May.

OPEC has not officially increased output since a meeting last September and has no plans to meet formally until September 9.

POLITICAL TENSION

Iran, OPEC's second biggest producer, has been locked in a dispute with the West over its nuclear program. Oil prices have been driven higher since mid-June as speculation has mounted that Israel could launch an attack on Iran's nuclear plants, which Tehran insists are purely for peaceful purposes.

The market is concerned any conflict could disrupt oil shipments from the Gulf through the vital Strait of Hormuz.