and acquisitions of additional acreage that may increase our working interest in these 38 locations as well as increase our operated acreage. 

We also have a non-operated position of approximately 6,700 net acres in the Midland Basin of west Texas, located in Howard, Glasscock, Martin and Midland counties, Texas. As of December 31, 2018, we had an interest in 100 gross vertical and 26 gross horizontal non-operated producing wells with an average working interest of approximately 36%. 

We have identified 366 potential gross horizontal non-operated drilling locations in various benches of the Wolfcamp and Spraberry formations with an estimated average working interest of approximately 25%. 

## Eagle Ford Trend 

As of December 31, 2018, we held approximately 29,000 gross (14,100 net) operated leasehold acres in Fayette, Gonzales and Karnes counties, Texas. The acreage is located in the crude oil window of the Eagle Ford shale trend of south Texas and is prospective for the Eagle Ford, Austin Chalk and Upper Eagle Ford formations. We serve as the operator with working interests ranging from approximately 17% to 67%. 

As of December 31, 2018, we operated 93 gross Eagle Ford wells and 13 gross Austin Chalk wells and had non-operated interests in approximately five gross producing Eagle Ford wells and one gross producing Austin Chalk well. We have identified a total of 68 potential gross Eagle Ford drilling locations in this acreage. In addition, because our acreage position is prospective for the Austin Chalk and Upper Eagle Ford formations, we may have additional future economic locations. The majority of our acreage is covered by an approximately 173 square mile 3-D seismic survey. 

## Oil and Natural Gas Reserves 

As of December 31, 2018, all of our oil and natural gas reserves were located in the state of Texas. We expect to further develop these properties through additional drilling and completion operations. Our reserve estimates have been prepared by Cawley, Gillespie & Associates, Inc. (“CG&A”), an independent petroleum engineering firm. The scope and results of CG&A’s procedures are summarized in a letter which is included as an exhibit to this report. For further information on estimated reserves, including information on estimated future net cash flows and the standardized measure of discounted future net cash flows, please refer to the Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited)  in Part II, Item 8 of the Notes to Consolidated Financial Statements of this report. 

As of December 31, 2018, our estimated proved reserves totaled 98,847 MBOE and had a PV-10 value of approximately $1,008.5 million (see Non- GAAP Reconciliation below) and a Standardized Measure of Discounted Future Net Cash Flows of approximately $959.5 million, all of which relate to our properties in Texas. We incurred approximately $153.2 million in capital expenditures, primarily drilling and completion costs, during 2018. We expect to further develop our properties through additional drilling. 

## 2018 Activity in Proved Reserves 

From January 1, 2018 to December 31, 2018, our total estimated proved reserves increased 24% from 79,976 MBOE to 98,847 MBOE. Of that, estimated proved developed reserves increased 18% from 19,961 MBOE to 23,646 MBOE and estimated proved undeveloped reserves increased 25% from 60,015 MBOE to 75,201 MBOE. These increases are primarily attributable to our successful drilling efforts in the Midland Basin, acquisitions and trades during the year, as well as improved commodity prices. 

## Proved Reserves as of December 31, 2018 

The below table sets forth a summary of our estimated crude oil, natural gas and natural gas liquids reserves as of December 31, 2018, based on the annual reserve estimate prepared by CG&A. In preparing this reserve report, CG&A evaluated 100% of our properties at December 31, 2018. Proved reserves are estimated based on the unweighted arithmetic average of the first-day-of-the-month price for each month within the 12- month period for the year. All prices and costs associated with operating wells were held constant in accordance with the SEC guidelines. 

Our proved reserve categories as of December 31, 2018 are summarized in the table below: 

