There are a variety of mechanisms to flexibly trade STA Capacity

You can offer or request capacity by posting a bulletin on our capacity bulletin board. Below are details of the mechanisms in place for trading this capacity. If you would like to know more, please contact us.


Existing shippers can sub-let all or part of their capacity to a third party, who will then become a sub-let shipper. Capacity is sub-let for a set period, from a minimum of 1 hour.  

The terms of a sub-let are negotiated and agreed between the two shippers. The sub-let shipper will then have to pay the original shipper for the capacity lease and all the running costs.

There is no contractual relationship between IUK and a sub-let shipper other than in relation to the use of ISIS®. The original shipper retains all obligations to IUK under the STA. 

If you're a new sub-let shipper, we will provide training in the use of ISIS® when you join - please allow time for this when agreeing trades. A shorter notice period is required for existing sub-let shippers who have already received training. We require just two hours' notice for sub-lets.

IUK's shippers have developed a suggested form of sub-let contract, the Interconnector capacity sub-let terms and conditions (SLTCs).


A shipper can assign all or part of their capacity to a new or existing shipper. Upon assignment, the assignee assumes all the rights and obligations related to the assigned capacity as defined in the STA for the remainder of the contract term. The assignee also obtains a share of pipeline inventory. A description of our contractual arrangements can be found in our summary of the STA.

Potential assignees are required to meet certain financial strength criteria.

IUK has developed standardised documentation to facilitate the assignment of capacity rights. It takes an average of eight weeks for the legal process to prepare and execute all the necessary formal documentation.


The pooling mechanism is designed to allows a number of existing shippers, each with small amounts of excess capacity, to aggregate that capacity into a more marketable quantity for sale to a third party. IUK does not maintain a capacity pool but will endeavour to match a third party requirement with existing shippers' unused capacity.

A third party shipper accessing IUK capacity through pooling will need to satisfy financial strength criteria and will be bound by the terms of the STA.  The pooled capacity will revert to the original shippers at the end of the pooling term.

Transfers between existing shippers 

Capacity transfers for existing IUK shippers are easy and straightforward to carry out via ISIS®. Capacity can be transferred with a two-hour lead time for periods of minimum duration of 1 hour.

This method of capacity trading is less formal than an assignment and can be implemented online by the counterparties at short notice. Capacity transfers are subject to the terms agreed between the relevant shippers.

IUK's shippers have developed a suggested standard form of capacity transfer contract which you are welcome to use. 

Inventory transfers between existing shippers 

As well as trading capacity, existing shippers can also trade gas, or inventory, within the transportation system. This is known as an inventory transfer.

Inventory transfers are easy and straightforward to carry out via ISIS®. Inventory can be transferred with a two-hour lead time.