When using your card at a gas station the gas station will authorize $75+ on your card and will then settle for the amount you purchased. The pending authorization can take 24-48 hours to expire. The actual amount authorized will vary by gas station.
When using your card at a restaurant the restaurant will authorize up to 20% more than the original charge to account for any tip and will then settle for the amount you authorized. The pending authorization can take 24-48 hours to expire.
When using your card at a hotel or rental car agency the merchant will authorize up to 15% on your card and will then settle for the amount you pay the agency or hotel. This hold can take up to 30 business days to expire.