Thanks for your question!
The answer is: It depends! It depends on a number of factors actually, the main two being the data feed you are using and the platform you are executing orders through. The question for you is, do you have a platform and data feed in mind that you would like to use? If so, we will be able to answer whether or not OCO orders are held server-side or locally on your machine.
To give you a few general answers on the data feeds and platforms we offer:
The Rithmic data feed and Rithmic’s own platforms (R Trader and R Trader Pro) utilize both server side bracket and OCO orders. There are also several third-party platforms that can utilize the Rithmic data feed that also support server side orders such as MultiCharts.
All CQG Native Platforms (CQG Desktop, Q Trader, Integrated Client) support server side bracket and OCO orders as well!
There are so many different combinations of platforms and data feeds, it would help us a ton if you narrowed down your options for us!
Thanks for the question,
Optimus Futures Support