In a statement late on Sunday, the firm also said it had reached a preliminary deal with creditor banks to restructure its debt and hoped to reach a final accord in early September.
Colonial said its debts totalled 8.99 billion euros as of June, while its assets were worth 10.5 billion euros.
"The company intends to continue talks with creditor banks with the aim of reaching a formal and binding accord for the complete financial debt restructuring," Colonial said in a statement.
The banks took partial control of Colonial earlier this year when some of its shareholders failed to meet obligations.
Colonial did not say which of its assets would be affected by the restructuring deal.
