UK GAS-Within-day gas rises as supplies from Norway, LNG drop

* System undersupplied by 5.5 mcm

* LNG flows sharply reduced

May 11 (Reuters) - British prompt gas prices were mixed on Wednesday as gas for immediate delivery rose in reaction to a slight shortfall in supply and day-ahead gas inched down due to a comfortable supply outlook for the rest of the week.

Gas for immediate delivery was up 0.35 pence at 30.25 pence per therm at 0943 GMT from the previous settlement, while gas for day-ahead delivery was down 0.15 pence to 30.15 p/therm.

Supplies were lower than levels on Tuesday due to a steep fall in Norwegian imports and the end of high-flow testing at the South Hook liquefied natural gas (LNG) terminal.

Britain's gas system was undersupplied by 5.5 million cubic metres (mcm) with flows forecast to be around 211.2 mcm/day, according to National Grid (LSE: NG.L - news) data.

Imports through the Langeled pipeline from Norway fell by 12 mcm to 28 mcm/day. Deliveries from South Hook LNG terminal plunged to 21 mcm/day from 73 mcm/day on Tuesday after high-flow testing at the terminal finished.

"Prices across the NBP (Shanghai: 601018.SS - news) (National Balancing Point hub) have opened the session largely in line with Tuesday's close, with supply outlooks over the coming weeks looking largely comfortable," said Andrew Crabtree, an analyst at Wingas.

Deliveries from South Hook LNG plunged to 21 mcm/day from 73 mcm/day on Tuesday after high-flow testing at the terminal finished.

In the Netherlands, the day-ahead gas price at the TTF hub fell by 0.05 euro to 12.77 euros per megawatt hour. In the European carbon market, front-year allowances eased by 0.02 euro to 5.88 euros a tonne. (Reporting by Oleg Vukmanovic; editing by Nina Chestney)