(Sharecast News) - BP smashed forecasts on Tuesday as second-quarter underlying profits more than doubled on the back of a surge in oil prices, but acknowledged that its operational performance "fell short" of expectations, with upstream plant reliability and refining throughput both lower.

The energy major reported an underlying replacement cost profit of $5.73bn for the three months to 30 June, up from $3.20bn in the first quarter and $2.35bn the year before. The consensus forecast was $5.01bn.

Bottom-line growth was driven by higher liquids and gas realisations including the impact of price lags, stronger realised refining margins and a stronger customers result,

Write-offs were due to the sale of Bay du Nord in Canada, the divestment of the Culzean gas field in the UK North Sea, and lower production.

"This is my first full quarter at bp, and it has been marked by one of the most disrupted periods in the global energy market," said boss Meg O'Neill.

O'Neill said the company delivered a "strong quarter" financially, and made good progress strengthening the balance sheet, adding: "But there are areas where our performance fell short."

"Operationally, our plants didn't run as well as they did last quarter - upstream plant reliability was 92.4%, compared to 95.7%, and production was down and our refineries processed less crude. This was due, in part, to planned maintenance and the conflict in the Middle East, but this is a reminder that we have more to do to deliver consistent operational performance."

O'Neill flagged several areas for the company to improve, including portfolio simplification, greater capital discipline and better cost efficiency.

"Our performance over the past few years has not met our own expectations, let alone those of our shareholders. We have not delivered consistently; we have written off too much value; and our costs and liabilities are not resilient enough in a low price environment," she said.

BP also announced its intention to sell its US biogas business Archaea as it continues to pivot out of renewables and simplify the business. That follows recent moves to sell its Gelsenkirchen refinery in Germany and retail business in Austria, along with the planned divestment of it North Sea business in the UK.