Mighty River Power quarterly operating update for the period ending 31 December 2010

MARKET ANNOUNCEMENT 21 January 2011 Three-month Operating Information to 31 December 2010 Mighty River Power Operating Information

3 months to 31 Dec 2010

3 months to 31 Dec 2009

402,000

400,000

Residential FPVV*

587

609

Commercial FPVV*

532

563

Spot

548

525

Net CFD

198

321

$105.00

$98.81

1,734

1,763

$64.70

$59.54

1,024

1,137

Geothermal (GWh)**

566

305

Co-generation (GWh)

84

144

0

5

1,674

1,591

$61.41

$59.20

Electricity Customers Sales (GWh)

Weighted Average Price FPVV* ($/MWh) Purchases Total NZEM (GWh) Weighted Average Cost ($/MWh) Generation Production Hydro (GWh)

Biomass (GWh) Total (GWh) Weighted Average Price ($/MWh) *FPVV: Fixed Price Variable Volume ** Calculated on an equity share basis

Mighty River Power’s total generation volumes for the three months to 31 December 2010 were up 5% on the same period in 2009 at 1,674GWh. The increase was primarily due to the contribution of the Nga Awa Purua Joint Venture’s 140MW Geothermal Power Station, commissioned in April 2010, which saw geothermal volumes (calculated on an equity share basis) rise 86% on the prior comparable period.

The period was characterised by rapid changes in hydrology and wholesale market conditions. Lake Taupo storage was near the top end of our operating range at the beginning of the quarter but dropped away steadily from October, to the extent that a drought was declared in the Waikato region in mid-December.

Hydro production was down 10% on the prior comparable period as a result of low inflows to the catchment during the drought, which ended late in December with substantial rainfall.

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Spot prices were low at the beginning of the quarter, but spiked in early December as a result of scheduled and unscheduled outages at other generators’ plants and South Island hydro generators storing water ahead of the typically dry summer months. In response to dry conditions and high prices, Mighty River Power briefly increased production from its flexible gas-fired Southdown Power Station. However, total Southdown volumes for the quarter were down 42% on the prior comparable period. Volume weighted average price for all generation production was $61/MWh over the quarter, slightly up on $59/MWh in the prior comparable period.

Electricity customer numbers were 402,000 at the end of December, up by 2,000 on the prior comparable period, but down from a peak of 412,000 at 30 June 2010. The decline in numbers is due to continuing high levels of retail competition, which intensified with changes to the market resulting from the Electricity Industry Act 2010. These changes are driving other generator/retailers to rebalance their retail customer bases between the North and South Islands. After a period of rapid growth in customer numbers Mercury Energy is focussing on maintaining a market share of around 20%, which we achieved during the quarter.

During the quarter the Company’s Tiny Mighty Power retail brand established a presence in Marlborough, the Wairarapa and North Canterbury, and the Bosco Connect brand extended into the Wellington apartment market.

ENDS For further information, please contact: David Glendining Head of Communications Mighty River Power Tel: 09 308 8259 Mob: 027 210 5337

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