The program that offers an opportunity to pay up without facing penalties, interest or possible legal action ends at midnight Friday.
Those who come forward and file past-due returns or have an underreported liability may pay their taxes in full or enter into an approved payment plan. All balances must be paid in full by June 30, 2010.
Delaware officials have said they hope to gain about $10 million in revenue that otherwise might be lost. They believe it had been more than 25 years since the state had offered a tax amnesty.