Latest 10 Orders - why Order IDs not sequential?

When my client looks at the Latest 10 Orders list in the admin Dashboard the Order IDs are not sequential.
She is very concerned that some orders could be missing.

Why are the numbers not sequential? Is it due to incomplete or aborted orders?

That is an impossibility. The order_id field is auto incrementing and a field that is shared by "all" customers. Knowing this, some customers may generate an order that will jump ahead of another person and vice verse.
In short, the orderID keeps generating in increments of +1 so if a customer makes an order on March 3rd 2012 with order ID 90, and then another order on April 4th 2012 their order id WILL NOT BE 91. Unless, that is, your store is suffering and you have had no orders in a month:)

it is due to incomplete / aborted orders, an order is generated once you reach the confirm section of the checkout process. On the admin panel you can select 'Missing Orders' from the status to view those orders, this is done like this to prevent the system from loosing orders.

Tcalp wrote:it is due to incomplete / aborted orders, an order is generated once you reach the confirm section of the checkout process. On the admin panel you can select 'Missing Orders' from the status to view those orders, this is done like this to prevent the system from loosing orders.

Perfect, thank you.