The decline was mainly due to a drop in client activity and a slump in trading performance in the energy sector, financial industry analytics firm Coalition said in a report.

Revenue from commodity trading, selling derivatives to investors and other activities in the sector fell to $1.3 billion (997.16 million pounds) in the first six months of the year, it said.

"Revenues reached their lowest level since 2006 because of ongoing weakness in energy, in particular natural gas, owing to lower volatility, reduced client activity and trading underperformance," Coalition said.

The company has been analysing bank data since 2006.

Coalition did not mention any individual banks, but in the second quarter, Goldman Sachs Group Inc (>> Goldman Sachs Group) posted the weakest commodities results in its history as a public company.

Banks' commodity revenue has been on a steady downward path in recent years as they have exited or slimmed down their commodity business due to heightened government regulation and poor performance from the sector.

In the fourth quarter of 2016, commodity revenue jumped 20-25 percent, largely due to an improvement in U.S. power and gas activity. But it declined 7 percent for the whole of 2016 due to weakness in the oil sector.

Coalition tracks Bank of America Merrill Lynch (>> Bank of America), Barclays (>> Barclays), BNP Paribas (>> BNP Paribas), Citigroup (>> Citigroup), Credit Suisse (>> Credit Suisse Group), Deutsche Bank (>> Deutsche Bank), Goldman Sachs, HSBC (>> HSBC Holdings), JPMorgan (>> JP Morgan Chase & Company), Morgan Stanley (>> Morgan Stanley), Societe Generale (>> Société Générale) and UBS (>> UBS Group).

(Reporting by Eric Onstad; Editing by Mark Potter)