They set the price high and they withheld a certain amount of propane from the market, allegedly.

NPR: Marketplace Report: BP Sued for Propane Profiteering

You may also have to pay estimated tax if the amount of income tax being withheld from your salary, pension, or other income is not enough.

FORBES: Taxes From A To Z (2013): A Is For Annualized Income Installment Method