The Omani Rial is the only currency widely accepted in the country, although you can use credit cards pretty much anywhere apart from the smallest market stalls.
ATMs will dispense cash for UK Visa and Cirrus cards, although the charges can be quite high, and often the best way to get local currency is by using exchanging traveller's cheques and shopping around for the best rate.
Most prices are fixed in Oman, and the only place where you'll be able to do any bargaining over goods is at the souks, although even there you're unlikely to get much off.
At the more touristy hotels in Muscat, tipping is increasingly expected, and 10% is appropriate where no service charge is already on the bill.
