Tighter gross margins at the company that operates the State’s only oil refinery resulted in the firm recording a pre-tax loss of $34.4m (€26.9m) last year.
The loss at Philips 66 Whitegate Refinery Ltd follows the firm’s $17.7m pre-tax profit in 2010.
The negative swing of $52m came in spite of revenues soaring by 33% from $2.19bn to $2.92bn last year.
The facility at Whitegate, in Cork, last year refined 2.91 million tonnes of crude oil imported from the North Sea and North and East Africa. The company swung into the red due to its cost of sales increasing by 37% from $2.1bn to $2.9bn in the 12 months to the end of December.
The directors’ report states: "The impact of turnover and cost of sales figures is that a gross loss of $4.6m was generated in 2011 compared to a gross profit of $51.1m in 2010.
"We continued to face an environment of weak energy demand, commodity price volatility and a global economic recession as a result of the financial turbulence. As such, the group was subjected to a challenging refining environment.
"Despite the volatile market environment, the group continued to perform strongly from an operational standpoint."
The company was renamed Phillips 66 earlier this year after its US parent, ConocoPhillips, announced that it was going to hive off its refining assets, including its Cork operations, into a separate company.
ConocoPhillips acquired the refinery in 2001 following its acquisition of another US oil company, Tosco.
The Irish unit is now wholly owned by Phillips 66 Inc and the numbers employed at the refinery remained static last year at 156, with staff costs increasing from $27.7m to $28.8m.
Aggregate remuneration to the four directors, including pension contributions, rose from $1.199m to $1.448m.
The figures also show that the firm recorded an operating loss last year of $24m, compared to an operating profit of $29.8m in 2010.
Net interest payments of $10.4m resulted in the pre-tax loss of $34.4m. A tax credit of $797,000 resulted in a post-tax loss of $33.6m.
The firm stated that it continues to invest in site infrastructure to enhance profitability and operating reliability. This includes a $36m investment to construct an amine and sulphuric acid plant that reduces the site’s environmental footprint as well as enabling the site to run higher-sulphur, more profitable crudes.
Accounts filed by a separate Phillips 66 subsidiary, Phillips 66 Bantry Bay Terminal Ltd show that it recorded a pre-tax profit of $14.9m after revenues marginally increased from $35.4m to $36.3m.
The main activity of the firm is the operation of the Whiddy oil terminal in Bantry, Co Cork.