1. http://nodal.ercot.com 1 Market Trials Update NATF May 4, 2010

2. http://nodal.ercot.com 2 Agenda General Reminders / Updates Phase 4 in Review 90 Day Look Ahead

3. Market Trials 2010 Roadmap http://nodal.ercot.com 3

4. General Updates / Reminders Reminder: Weekly Friday Market Call Changes –ERCOT will be adjusting the agenda, effective 5/7/2010 09:00 AM-09:30 AM Outage Scheduling 09:30 AM-10:00 AMCongestion Revenue Rights 10:00 AM-11:00 AM Day Ahead Market / RUC / SASM 11:00 AM-12:00 PMReal Time Market / LFC 12:00 PM-01:00 PMBreak 01:00 PM-02:00 PMSettlements and Billing / COMs –The weekly Monday kick off meeting will remain in place, unchanged Environment Availability for May 2010 –The Nodal Production Environment will be available Monday – Friday from 8am – 6pm for all systems except EMS / SCADA and SCED –EMS / SCADA and SCED will continue to be monitored, maintained and available 24x7 –ERCOT will continue to submit test transactions to verify and performance test systems –Additionally, ERCOT will also begin the process of testing fail-overs. Initially, this will be during non-business hours Once the process is matured, we will perform these during business hours Test date / times will be communicated on Friday market calls so that MPs may also test their own failure process Reminder: ERCOT is looking for suggestions for additional Operational Scenarios –Send these to markettrials@ercot.commarkettrials@ercot.com –Deadline for submissions is 5/17/2010 http://nodal.ercot.com 4

5. http://nodal.ercot.com 5 Phase 4 in Review Day Ahead Market –Participation levels: 169 / 265 QSEs actively participating in the Day Ahead Market >50% of the 7 / 265 are newly registered and ramping up 45 / 265 are participating under the 50% requirement 44 / 265 are not participating –Cleared 9 Market-Facing Day Ahead Markets and ran DRUC, SASM and HRUC Telemetry update –ERCOT continues to reach out to TSPs and QSEs on telemetry issues –260 QSE telemetry points Mostly due to incorrect ownership information 145 of these will be corrected in the next model load –357 TSP telemetry points 288 of these are being worked by the TSPs The remainder fall into the following categories: ERCOT investigating, considered “future” points and ownership issues Expect resolution of most points by 5/10/2010 –Quality (ICCP server to server only) TSP Quality currently has 1356 suspect points: 97.9% Good overall QSE Quality currently has 871 suspect points: 94.9% Good overall

6. http://nodal.ercot.com 6 Phase 4 in Review Real Time Market (continued) –Submissions >95% of the expected TPOs are consistently submitted –Individual LFC tests 23 tests conducted in MT4 10 additional tests are scheduled prior to the 5 / 7 timeline Model / Data Update –Delayed the start of weekly updates (currently on bi-weekly updates) –Continue to work on registration data CRR –Monthly Auction ran and invoiced as planned –Initiated Bid Window for Multi-Month Auction Settlements Began on time for DAM / RTM Operating 4/21/2010

7. Phase 4 in Review Primary issues with DAM / RUC coming out of Phase 4 –Bid/Offer IDs with special characters QSEs do not submit special characters until resolved This will be included in 1.19L ETA early June –MMS subroutines having issues with certain combinations of decimals in clearing process The suspected root cause was that 2 QSEs had identical bids Will be fixed in emergency patch from vendor in approx. 1 week –Circuit Breaker outages seen as always ‘Open’ Fixed in MMS Patch 7 – ETA TBD –MMS numbers the main network incorrectly when integrated with outages (depends on combination of outages). Included in the emergency patch in approx 1 week http://nodal.ercot.com 7

8. 90 Day Outlook : May Market Activities Functional Area Real-Time Market Congestion Revenue Rights Day-Ahead Market Reliability Unit Commitment Outage Scheduler COMS/Settlements Network Modeling Nodal Reports Credit Full Integration Targeted Activities for May 2010 ERCOT ramps to DAM / DRUC 5x / weekly 2hr LFC closed loop test executed ERCOT complete Balance of Year auction ERCOT executes June Monthly CRR Auction ERCOT releases credit integration SASM executed as needed ERCOT executes limited HRUC ERCOT ramps to reflect protocol timelines on a best effort basis JanFebMarAprMayJuneJulyAug

9. 90 Day Outlook : June Market Activities Functional Area Real-Time Market Congestion Revenue Rights Day-Ahead Market Reliability Unit Commitment Outage Scheduler COMS/Settlements Network Modeling Nodal Reports Credit Full Integration Targeted Activities for June 2010 Operational scenarios executed 8hr LFC closed loop test executed ERCOT executes July Monthly CRR Auction DAM / DRUC Continues 5x / weekly SASM executed as needed ERCOT executes limited HRUC Protocol timelines on a best effort basis JanFebMarAprMayJuneJulyAug

10. 90 Day Outlook : July Market Activities Functional Area Real-Time Market Congestion Revenue Rights Day-Ahead Market Reliability Unit Commitment Outage Scheduler COMS/Settlements Network Modeling Nodal Reports Credit Full Integration Targeted Activities for July 2010 Exercise ‘Normal State’ processes and procedures, including weekends 48hr LFC closed loop test executed DAM / DRUC executes 7x / weekly for two weeks ERCOT executes HRUC 7x24 during 7 day weeks Protocol timelines during 7 day weeks ERCOT executes August Monthly CRR Auction SASM executed as needed JanFebMarAprMayJuneJulyAug

11. http://nodal.ercot.com 11 Q&A Q&A / Open Forum