Word’s out today that PayPal is trying out another expansion into the world of brick-and-mortar stores.

Earlier this month we reported on a pilot program at 5 Home Depot stores in which payments via PayPal were being tried out. The program is now reported to have been rolled out at 51 Home Depots. PayPal is expected to offer the payment option at 20 major retailers by the end of this year.

Office Depot appears to be the next major retailer on the list. Reuters is reporting today that the program is now being tested out at a small number of the office supply stores. Office Depot sounds cautious about the new program. They are reported to be walking it out “very, very slowly.”

The idea behind the program is to allow shoppers to pay for their merchandise without a card or cash being required. It’s being called ‘wallet in the sky.’ The shopper just enters their phone number and the personal identification number (PIN) into a keypad, and the funds are withdrawn from their PayPal account. Shoppers would also be able to use a PayPal debit card as another form of payment.

In the past, PayPal has only processed online transactions. The Home Depot and Office Depot programs are the first time that PayPal has moved their transaction service into the field. They are also said to be working on a smart phone app for making in-store PayPal transactions.