The oil junior, focussed on Nigeria, said it is issuing 166.6mln new shares priced at 0.3p each.
Cash raised in the placing will be used for general working capital, allowing the group to continue efforts to secure project financing for the Ororo field.
“The directors continue to carefully manage the working capital position of the company and additional capital may be required depending on the timing of raising project funding,” Sirius said in a statement.
“The directors will update shareholders in due course on such funding and whilst they remain positive of a successful outcome, no guarantees can be given.
On AIM, Sirius Petroleum shares were down 13.3% trading at 0.33p each.