Exhibit 23.4



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|LOGO |  | Collarini Associates
3100 Wilcrest Drive, Suite 140 Houston, Texas
77042 Tel. (832) 251-0160
www.collarini.com

March 2, 2011

Mr. Jerry Kennedy

ATP Oil & Gas Corporation

4600 Post Oak Place, Suite 200

Houston, Texas
77027-9726

Dear Mr. Kennedy:

In accordance with your request and to enable ATP Oil & Gas Corporation (ATP) to satisfy the requirements of ATPs annual reporting, we have
estimated the proved reserves and future revenue, as of January 1, 2011, to the interest of ATP in and related to certain oil and gas properties, located in the Gulf of Mexico and in the North Sea. The estimate of proved reserves and the future
revenue therefrom conform to all standards and definitions promulgated in Section 210.410 of Regulation S - X issued by the Securities and Exchange Commission in November 1988 and amended in December 2008.

As presented in the accompanying detailed projections by reservoir and by reserve category, we estimate the net reserves and future net income to the ATP
Oil & Gas Corporation interest, as of January 1, 2011, in the Gulf of Mexico, to be:



|                 |  |                       |        |  |                        |  |         |              |  |  |                     |  |  |  |           | 
|---------------- |  | --------------------- | ------ |  | ---------------------- |  | ------- | ------------ |  |  | ------------------- |  |  |  | --------- | 
|                 |  | Net RemainingReserves |        |  | Future Net Income (M$) | 
|Reserve Category |  | Oil(MBO)              |        |  | Gas(MMCF)              |  |         | Undiscounted |  |  | PresentWorth at 10% | 
|Proved           |  |                       |        |  |                        |  |         |              |  |  |                     |  |  |  |           | 
|Producing        |  |                       | 9,683  |  |                        |  | 25,356  |              |  |  | 795,837             |  |  |  | 703,244   | 
|Shut-In          |  |                       | 1,584  |  |                        |  | 3,120   |              |  |  | 103,256             |  |  |  | 79,277    | 
|Behind Pipe      |  |                       | 1,844  |  |                        |  | 21,273  |              |  |  | 173,890             |  |  |  | 94,467    | 
|Undeveloped      |  |                       | 35,724 |  |                        |  | 153,067 |              |  |  | 2,042,064           |  |  |  | 1,299,753 | 
|P&A              |  |                       | 0      |  |                        |  | 0       |              |  |  | -114,662            |  |  |  | -42,054   | 
|                 |  |                       |        |  |                        |  |         |              |  |  |                     |  |  |  |           | 
|Total Proved     |  |                       | 48,836 |  |                        |  | 202,815 |              |  |  | 3,000,385           |  |  |  | 2,134,687 | 

As presented in the
accompanying detailed projections by reservoir and by reserve category, we estimate the net reserves and future net income to the ATP Oil & Gas Corporation interest, as of January 1, 2011, in the North Sea, to be:



|                 |  |                       |        |  |                        |  |         |              |  |  |                     |  |  |  |         | 
|---------------- |  | --------------------- | ------ |  | ---------------------- |  | ------- | ------------ |  |  | ------------------- |  |  |  | ------- | 
|                 |  | Net RemainingReserves |        |  | Future Net Income (M$) | 
|Reserve Category |  | Oil(MBO)              |        |  | Gas(MMCF)              |  |         | Undiscounted |  |  | PresentWorth at 10% | 
|Proved           |  |                       |        |  |                        |  |         |              |  |  |                     |  |  |  |         | 
|Producing        |  |                       | 4      |  |                        |  | 8,323   |              |  |  | 41,330              |  |  |  | 31,667  | 
|Undeveloped      |  |                       | 25,618 |  |                        |  | 93,118  |              |  |  | 1,320,421           |  |  |  | 428,573 | 
|P&A              |  |                       | 0      |  |                        |  | 0       |              |  |  | -25,111             |  |  |  | -8,636  | 
|                 |  |                       |        |  |                        |  |         |              |  |  |                     |  |  |  |         | 
|Total Proved     |  |                       | 25,621 |  |                        |  | 101,441 |              |  |  | 1,336,640           |  |  |  | 451,604 | 



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ATP Oil & Gas Corporation

March 2, 2011

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Oil volumes are generally expressed in thousands of stock tank barrels (MBO), where one barrel is
equivalent to 42 United States gallons. Gas volumes are expressed in millions of standard cubic feet (MMCF) at 60 degrees Fahrenheit and the contract pressure base.

Net sales, as defined in this report, are before deducting production taxes. Net income is after deducting these taxes, and after deducting future capital costs and operating expenses, but before
consideration of federal income taxes. The future net income has also been shown discounted at ten percent to determine its present worth as required by Regulation S-X. This present worth is included to indicate a standard measure and is not
intended to represent the market value of the property. Our estimates of future cash flows include estimates of all costs required to recover reserves.

Reserves in this report were estimated using all applicable engineering and geological data available such as, but not limited to, historic production volumes, initial flow test information, flowing
tubing pressures, shut-in tubing pressures, bottom hole pressures, repeat formation test data, pressure- volume- temperature fluid analysis, geological well logs, sidewall core analysis, and whole core analysis at the time the report was conducted.

The reserve volumes and their respective classifications and categorizations were estimated by performance methods, volumetric methods,
analogy, or combination of methods. Performance methods generally included decline curve analysis and material balance analysis where representative data was available. Volumetric estimates generally included a combination of geological and
engineering interpretations, while analogy methods included reserve estimates from historical performance of similar wells and reservoirs in the field or nearby fields.

Proved reserve classifications were determined based on the reasonable certainty of recovering the estimated volumes or more. The proved reserve categorizations were based on the stage of
maturity and development of the respective proved reserves.

Based on gross oil equivalent barrels, approximately 60 percent of ATPs
proved reserves are located in the North America, United States, Gulf of Mexico and 40 percent are located in the United Kingdom sector of the North Sea. ATPs proved reserves are approximately 19 percent developed and 81 percent undeveloped in
total. The Gulf of Mexico reserves are approximately 22 percent developed and 78 percent undeveloped. The United Kingdom reserves are approximately 12 percent developed and 88 percent undeveloped.

ATPs Gulf of Mexico proved developed reserves are approximately 63 percent proved producing and 37 percent proved non- producing. Approximately 41
percent of the Gulf of Mexicos proved producing reserves were estimated by performance methods and 59 percent were estimated by volumetric methods. The proved non-producing reserves were estimated 24 percent by performance methods and 76
percent by volumetric methods, while 98% of the proved undeveloped reserves were estimated by volumetric methods. These estimates are based on gross oil equivalent barrels that ATP holds an interest in.

ATPs North Sea proved developed reserves are 100 percent proved producing. Approximately 89 percent of the North Seas proved producing
reserves were estimated by performance and 11 percent were estimated by analogy. Approximately 37 percent of the proved undeveloped reserves in the North Sea were estimated by performance methods, 33 percent were estimated by volumetric methods and



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ATP Oil & Gas Corporation

March 2, 2011

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30 percent were estimated by analogy. These estimates are based on gross oil equivalent barrels that ATP
holds an interest in.

A detail description of methodology used in estimating reserves for each well and reservoir in each field is tabulated
in the respective field section under Reserve Summary included in the detailed report.

Hydrocarbon prices used in this report are
based on SEC price parameters using the average prices received on the first of each month during the 12-month period prior to the ending date of the period covered in this report, determined as an unweighted arithmetic average of the
first-day-of-the-month price for each month within such period. The product prices used to determine future gross revenue for each field were determined by applying benchmark pricing as describe above then adjusted by differentials only
to the extent provided by SEC guidelines. These differentials generally adjust the benchmark prices on a field by field basis to account for product quality, transportation, and marketing. The differentials were provided to
Collarini Associates in detail from ATP. Collarini accepted the differentials as factual data and did not confirm the accuracy of these adjustments. The following table summarizes by major geographic region the average benchmark
prices and the average realized price after the appropriate differentials were applied.



|                            |  |         |                |  |                |  |                    |                    |  |   |                   |  |  |   |           | 
|--------------------------- |  | ------- | -------------- |  | -------------- |  | ------------------ | ------------------ |  | - | ----------------- |  |  | - | --------- | 
|Geographic Region           |  | Product |                |  | PriceReference |  |                    | Avg BenchmarkPrice |  |   | Avg RealizedPrice | 
|                            |  |         |                | 
|North America
United States |  |         |                |  |                |  |                    |                    |  |   |                   |  |  |   |           | 
|Gulf of Mexico              |  |         | Oil/Condensate |  |                |  | WTI Cushing        |                    |  | $ | 79.43/bbl         |  |  | $ | 78.78/bbl | 
|                            |  |         | Gas            |  |                |  | Henry Hub          |                    |  | $ | 4.38/MMBtu        |  |  | $ | 4.71/Mcf  | 
|                            |  |         |                | 
|United Kingdom
North Sea    |  |         | Oil/Condensate |  |                |  | Brent Oil          |                    |  | $ | 79.71/bbl         |  |  | $ | 76.71/bbl | 
|                            |  |         | Gas            |  |                |  | Heren Index (BNBP) |                    |  | $ | 6.58/MMBtu        |  |  | $ | 6.26/Mcf  | 

Future development costs included in
this report were provided to Collarini Associates by ATP and accepted as factual data. Collarini Associates reviewed, for reasonableness, the estimated future development cost, plug and abandonment cost and their respective timing for each well,
reservoir, and field. Collarini did not, however, confirm the accuracy of these expenditures. These costs are tabulated in the respective field section under Forecast of Expenditures included in the detailed report. These costs are held
constant and not escalated. It should be noted, as provided by ATP, the value of the ATP Innovator floating platform, located at Mississippi Canyon 711, and its associated infrastructure, is $272,932 million as of December 31, 2010. The
value is depreciated using a straight-line depreciation method over its estimated useful life. The depreciated book value is reflected in the appropriate proved category.

Operating costs are based on actual expenses, as provided by ATP Oil & Gas Corporation. Collarini did not confirm the accuracy of these expenses. These current expenses are held constant through
the life of the property. These costs include processing fees where applicable. Estimated lease fuel-gas usage has been included as a reduction to produced volume in the cash flow forecast.

Collarini Associates utilized all data, appropriate methods and procedures deemed necessary to conduct and finalize this report to conform to all standards and definitions promulgated in
Section 210.4-



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ATP Oil & Gas Corporation

March 2, 2011

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10 of regulation S  X issued by the Securities and Exchange Commission in November 1988 and
amended in December 2008.

The reserves presented in this report are estimates only and should not be construed as being exact quantities. They
may or may not be recovered, and if recovered, the revenues, costs, and expenses therefrom may be more or less than the estimated amounts. Because of governmental policies, uncertainties of supply and demand, and international politics, the actual
sales rates and the prices actually received for the reserves, as well as the costs of recovery, may vary from those assumptions included in this report. Also, estimates of reserves may increase or decrease as a result of future operational
decisions, mechanical problems, and the price of oil and gas.

All reserve estimates have been performed in accordance with sound engineering
principles and generally accepted industry practice. As in all aspects of oil and gas evaluation, there are uncertainties inherent in the interpretation of engineering data, and all conclusions represent only informed professional judgments.

The titles to the properties have not been examined by Collarini Associates, nor has the actual degree or type of interest owned been
independently confirmed. The data used in our estimates were obtained from ATP Oil & Gas Corporation and from sources which provide publicly accessible data and are considered accurate.

A detailed environmental and mechanical inspection of the properties was not made by Collarini Associates. A visual inspection of the properties
themselves was not considered necessary for the purpose of this report. No assessment of compliance with environmental regulations or future liability for site remediation was made. We are independent consultants; we do not own any interest in this
property and are not employed contingent upon the value of this property. All engineering calculations and basic data used in the analysis are maintained on file in our office and are available for review.

Very truly yours,

COLLARINI ASSOCIATES

LOGO

/s/ Mitch Reece, P.E.

President

MCR/tlk

Collarini Engineering Inc.

Texas Board of Professional Engineers Registration F-5660