Now moving to Slide 4 of our presentation. The second quarter was very productive for Rex Energy. First, we are very excited to announce our Warrior Prospect in Carroll County, Ohio, where we are in the process of closing approximately 11,000 net acres subject to title perspective for the Utica Shale. We believe that this position lies within the wet gas window of the play and should provide Rex a good entry point into this portion of the Utica Shale play. This acreage acquisition, along with our Butler County operated acreage and a small position we hold in Mercer County, PA, would bring our total potential Utica Shale lease holds to approximately 83,000 gross acres and 58,000 net acres. We are currently drilling our first Utica Shale well in Butler County and hope to fracture stimulate it in the third quarter.In addition to our Carroll County acreage acquisition, we have also, during the quarter, leased an additional 3,700 net acres in our Butler operating area. This brings our total Marcellus Shale potential acreage to approximately 63,000 net acres with approximately 43,000 of this net acreage in our Butler operating area. Lastly, we have completed the drilling of our first Upper Devonian test well and have plans to fracture stimulate this well during the third quarter. We are also very pleased to announce that Rex Energy's bank group voted unanimously to increase our borrowing base from $160 million to $240 million, a 50% increase. This significant increase was the result of the company's continued development of additional proved undeveloped locations, improved well performance and increasing EURs. The bank group also agreed to extend the term of the credit facility for an additional 2 years through September 2015. And lastly, reducing the low end of our interest rate grid by 25 basis points.
I would like to say thank you to all those banks of the syndicated group for their continued support of Rex Energy.Moving to Slide 5. As evidenced by the increased borrowing base, the company continued its production growth in the second quarter with our average daily production increasing by 27% over the first quarter and 87% over the same period in 2010. Our average daily production was approximately 35.2 million cubic feet equivalent per day, which was 9% above our previous issued second quarter guidance. The increase is attributed to our accelerated drilling schedule, increased levels of production on our new wells, and the Sarsen cryogenic plant running efficiently in our Butler-operated areas. In addition, I would also like to thank our partners of the Williams companies and our JV area where they have had the same types of success growing production. Daily natural gas production increased 46% over the first quarter and daily production from natural gas liquids increased 80% over the first quarter. As discussed earlier, our accelerated drilling program and improving well results have boosted both our natural gas and NGL production. Taking a look at our production mix, oil and natural gas liquids accounted for 41% of our production during the quarter. Average daily oil production was down flat in the second quarter when compared to the first quarter of 2011. This was caused by weather-related issues in our large field in Illinois where flooding and other issues caused wells to be shut in during the quarter. Since then, all wells are now back online and producing and we expect oil production to increase to normal preflood levels. Our per unit lease operating expenses were 12% lower compared to the first quarter of the year. The lower per unit cost are a result of growing our production from the lower cost Marcellus Shale operations and becoming more efficient in the operations of these wells.
Lastly, but most important, our EBITDAX has increased 19% over the first quarter of the year and by 130% over the second quarter of 2010. This demonstrates the company's strong growth in operating cash flow to better well results and lower operating cost.Read the rest of this transcript for free on seekingalpha.com