I need a formula that will autosum the amount of work we have quoted for each client.

Our Purchase Order Numbers run numerically in column B, Client Name in column C and amount quoted in column D.

I need a formula that will pick up the client name (text in col. B), take the quote figure in column C and then autosum it into another cell (say in column G for client a, column H for client B and so on) so we have a running total for works quoted for each client as the new quotes are added to the spreadsheet.