Creating a large number of AWS EC2 instances

This is probably too simple a question, but how does one create many instances (in the low hundreds).

Our process can require up to ten instance/task and we can need to run up to a dozen instances.

However, the upper limit of instances we can run/account is 10-20.

Up until now, we have gone around this with multiple AWS accounts, which is creaky to say the least. We would prefer something more like a large cluster.

Is there a way of upping the limit programmatically, or does one have to make a special AWS request?

Thanks.