May 13 (Reuters) - U.S. energy firms likely added a near-normal 85 billion cubic feet (bcf) of natural gas into storage last week, according to the average estimate in a Reuters poll released on Wednesday.

The estimate compares with an injection of 109 bcf during the same week a year ago and an average increase of 84 bcf over the past five years (2021-2025) for the week.

In the prior week ended May 1, energy firms added 63 bcf of gas into storage. USOILN=ECI

If correct, the forecast for the week ended May 8 would increase stockpiles to 2.290 trillion cubic feet. That figure would be about 2.3% above the same week a year ago and 6.5% above the five-year average for the week.

The U.S. Energy Information Administration is scheduled to release its weekly storage report at 10:30 a.m. EDT (1430 GMT) on Thursday.

There were 65 total degree days (TDDs) last week, close to the 30-year normal of 66 TDDs for the period, data from financial firm LSEG showed.

Total degree days measure the number of degrees a day's average temperature is above or below 65 degrees Fahrenheit (18 degrees Celsius) to estimate demand to cool or heat homes and businesses.

Reuters polled 11 analysts, whose estimates ranged from injections of 78 bcf to 91 bcf, with a median increase of 85 bcf.

Early estimates for the week ending May 15 ranged from injections of 58 bcf to 101 bcf, with an average increase of 85 bcf.

Those figures compare with an injection of 119 bcf during the same week last year and a five-year average increase of 92 bcf.

Following is a list of poll participants. All figures are in billion cubic feet:

Organization	Forecasts in bcf
C H Guernsey	78
SMC Report	79
Gelber & Associates	83
Energy Ventures Analysis	84
Baker & O'Brien	85
Schneider Electric	85
StoneX Group Inc	85
Natural Gas Intelligence	86
Energy Aspects	87
Ritterbusch & Associates	89
DTN	91