An opportunistic throttling approach can be used for customers of shared resources in a multi-tenant environment. Each customer can have a respective token bucket with a guaranteed fill rate. When a request is received for an amount of work to be performed by a resource, the corresponding number of tokens are obtained from, or charged against, a global token bucket. If the global bucket has enough tokens, and if the customer has not exceeded a maximum work rate or other such metric, the customer can charge less than the full number of tokens against the customer's token bucket, in order to reduce the number of tokens that need to be taken from the customer bucket. Such an approach can enable the customer to do more work and enable the customer's bucket to fill more quickly as fewer tokens are charged against the customer bucket for the same amount of work.