Transactions pending authorisation on a credit card may be listed on your account for a few reasons. Companies like hotels and car rental agencies use this method to verify that there's enough money available to cover the transaction and any incidentals that might be accrued -- like room service or mileage fees. Petrol stations might list a pending transaction of a small amount when you swipe your card at the pump, then void the transaction when they charge you the full amount of your purchase.
Companies, like hotels or car rental agencies, check that enough funds to cover the transaction are available in your credit account by posting a partial transaction to your account. The amount pending authorisation (sometimes listed as a payment authorisation) may exceed the amount you intend or plan to pay. It's important to know this isn't the final charge, which can't be calculated until you're done with the service. This transaction is a method of verifying your credit and can effect your credit limit for the time it's listed as pending on your account.
Once you finish using the service and the actual amount is deducted from your credit account, the amount pending authorisation will be voided. It's possible that this could take three to five business days, depending on the company's policies. To check on a transaction listed as "pending authorisation," contact the company that initiated the charge before contacting your credit card company. Each company has its own policies regarding the way pending transactions are handled.
Restaurants might list an incorrect amount pending authorisation on your account when you are charged for your meal. This is because you may choose to leave a tip on your card as well, but those charges are usually not settled until close of business on any given day. Transactions like this are typically voided the same day (or the following business day), when the actual charge clears.
Other charges pending authorisation might be made anytime you swipe your card (or fill in your card information) prior to payment, such as transactions at the petrol pump. When you run your card prior to pumping, a payment is initiated on your account for a small amount that will be listed as pending. Once you finish the transaction, that initial pending charge should be voided.