1. http://nodal.ercot.com 1 Market Trials Congestion Revenue Rights Weekly Update May 21, 2010

2. http://nodal.ercot.com 2 Antitrust Admonition ANTITRUST ADMONITION ERCOT strictly prohibits Market Participants and their employees who are participating in ERCOT activities from using their participation in ERCOT activities as a forum for engaging in practices or communications that violate the antitrust laws. The ERCOT Board has approved guidelines for members of ERCOT Committees, Subcommittees and Working Groups to be reviewed and followed by each Market Participant attending ERCOT meetings. If you have not received a copy of these Guidelines, copies are available at the Client Relations desk. Please remember your ongoing obligation to comply with all applicable laws, including the antitrust laws. DISCLAIMER All presentations and materials submitted by Market Participants or any other Entity to ERCOT staff for this meeting are received and posted with the acknowledgement that the information will be considered public in accordance with the ERCOT Websites Content Management Operating Procedure.

3. http://nodal.ercot.com 3 Agenda Anti-trust Admonition Environment Report –Planned / unplanned outages –Known Issues Standing Reports and Updates –Future activities Question and Answers / General Discussion –FAQ –Credit Constraints ERCOT asks that Market Participants log into the WebEx session using their company name and then their name. This will allow ERCOT to take roll-call offline

4. Market Trials 2010 Roadmap http://nodal.ercot.com 4

5. http://nodal.ercot.com 5 Day-to-day operations summary: Planned / Unplanned Outages of EDS Planned Outages –Planned Outages No Planned Outages this coming week Unplanned Outages There were no unplanned CRR outages this week

6. Known Issues No new issues

7. http://nodal.ercot.com 7 Standing Reports and Updates: General reminders / updates June 2010 Auction –6416 bids/offers –6401 bids/ 15 offers –649 24-Hrs/ 1930 Off-peak/ 2245 PeakWD/ 1577 PeakWE

8. http://nodal.ercot.com 8 Standing Reports and Updates: General reminders / updates Next week’s activities –Results published Monday morning –Invoices out by Tuesday night –July Network Model Posted Friday –Ownership reflected by Friday night

9. http://nodal.ercot.com 9 Q&A FAQ/Follow Up

10. Q) When will ERCOT start posting actual CRR Network Models that they will use to allocate CRRs in Nodal? A) ERCOT will begin posting live models in early October after the 168 hour test. http://nodal.ercot.com 10

11. Q) The Credit Lock Date has passed. Can you allocate 25M to Account Holder XABC? A)With credit integration, we are no longer able to extend credit after the lock date. If you miss the credit window for one auction, please refer to the Market Trials Handbook at http://nodal.ercot.com/readiness/markettrials/crr/index.html http://nodal.ercot.com/readiness/markettrials/crr/index.html for the dates of the next scheduled auction. http://nodal.ercot.com 11

12. Q) If we want to increase our ACL while the credit window is open, how do we do so? A)You will need to submit an email to Markettrials@ercot.com requesting an ACL increase from Credit. For an email template, please refer to slide 17 of the COMS/Settlements/Credit Weekly Update slide deck for May 7, 2010.Markettrials@ercot.com http://nodal.ercot.com 12

13. Q)I noticed several instances in the attached spreadsheet where we were either not awarded any CRR quantities or the CRR bid was not fully awarded. In all instances, the bid was above the clearing price. Can you offer some insight into this? A) This was due to a budget constraint. While it is correct that if the binding constraint is a transmission element of some sort partially awarded bids clearing prices would equal their bid prices, that is not the case with binding budget constraints. We do not include budget constraints in the list of binding constraints available to market participants. It is our feeling that this is fairly confidential information that you would not want published. To check that your budget was properly binding you could… 1.Multiply all the awarded option bids by bid price by time of use hours, 2.Multiply all the awarded obligation bids (by absolute value of bid price + $1.5) then by time of use hours 3.Multiply all awarded sales with negative offer prices by bid price by time of use hours by negative 1. Add above together and see if it equals your auction budget. http://nodal.ercot.com 13

14. CREDIT CONSTRAINT in AUCTION Sale? Max(0,hrs*MW*-offer price) OPT? hrs*MW*bid pricehrs*MW*M*[ABS(Bid Price)+A] M & A TAC defined Current M = 1, A = 1.5 =IF(I3="SELL",MAX(0,-1*G3*F3*VLOOKUP(H3,hours,2,0)), IF(J3="OPT",G3*F3*VLOOKUP(H3,hours,2,0),F3*M*(ABS(G3)+A)*VLOOKUP(H3,hours,2,0))) Y N N Y

15. http://nodal.ercot.com 15 Q&A Q&A / Open Forum

16. Appendix http://nodal.ercot.com 16