Oil prices ended 2011 up 13 per cent as a fresh wave of supply concerns capped a year of unrest and disruptions in North Africa and the Middle East that overwhelmed concerns about the econ-omic health of large consuming nations. Iran\'s recent threats to shut the Strait of Hormuz, a vital oil shipping chokepoint, added another geopolitical threat to markets gripped throughout the year by the unrest of the Arab Spring, most notably shutting exports from Opec-member Libya. The supply problems helped lift the price of global benchmark Brent crude by 13.3 per cent on the year to average nearly $111 (Dh407) a barrel for 2011, eclipsing the previous annual record of nearly $100 struck in 2008 and marking the third year of annual gains. Volatile environment \"[The 2011 price gains] belied an extremely volatile pricing environment that saw [US] values drop to as low as $75 in early October after advancing to around $115 in early May,\" Jim Ritterbusch, president at Ritterbusch and Associates said in a note. US crude prices rose 8.2 per cent from the close of 2010, outperforming most other commodities tracked in the 19 commodities tracked on the Thomson Reuters-Jefferies CRB index that fell on the year. The average price for the year was about $95 a barrel. Market players said the factors that helped cap price gains in 2011 could continue into the new year. \"While a  test of the $75 level might appear out of reach in view of a variety of geopolitical uncertainties, we feel that global contagion off of a weakening Eurozone will be providing significant bearish impetus,\" Ritterbusch added. US heating oil futures were the top performer on the index, gathering strength from rising US exports and the impending closure of three of Petroplus\' five European refineries after lenders froze its credit lines last week. Heating oil gained over 15 per cent in 2011, while US RBOB gasoline futures rose by more than 9 per cent. On Friday, Brent February crude fell 63 cents to $107.38 a barrel, having swung from $106.62 to $108.25 in light holiday trade, weighed down by ongoing concerns about Europe\'s debt crisis and slowing Chinese factories. US February crude fell 82 cents to settle at $98.83 a barrel, having swung from $98.61 to $100.16. Trading was choppy on Friday and pressure came from data from the HSBC Purchasing Manager\'s Index showing factory activity in No 2 oil consumer China shrank again in Dec-ember as demand at home and abroad slackened. \"Weak Chinese data gave oil some pressure, but [US] prices are still in the $95-$100 area so the market needs to see continuing US economic growth and whether or not Europe can resolve its debt problems,\" said Gene McGillian, analyst at Tradition Energy in Stamford Connecticut. Watching Iran The market was also closely eyeing news Iran plans to fire long-range missiles during a naval drill in the Gulf yesterday. Tehran has threatened to close the Strait of Hormuz, through which more than a third of daily seaborne crude shipments pass, if the West imposes sanctions on its oil exports. The premium of Brent crude to US futures held above $8 a barrel in post-settlement trading on Friday, after blowing out to $28 a barrel in October. The resumption of Libyan exports has helped narrow the spread along expectations new pipeline plans will ease a glut of crude in the US mid-west that has weighed on US futures. Speculators hiked their net long positions in US crude oil futures and options positions in the week to Tuesday, data from the US Commodity Futures Trading Commission showed.