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Well Pressure Atlas

Offshore over-pressure (HPHT) and onshore under-pressure, from public data

One axis, two extremes. Offshore Gulf of Mexico Wilcox is extreme over-pressure — ultra-HPHT reservoirs to ~25,000 psi (Anchor; 23,000–27,000 psi disclosed). Onshore Mid-Continent gas is extreme under-pressure — a median of ~9% of hydrostatic with hundreds of near-vacuum wells. Same subsurface, opposite ends of one pressure axis.

Offshore max disclosed

~25,000 psi

Anchor (reservoir BHP)

Onshore wells screened

30,100

19,972 OK · 10,103 KS · 25 TX

Onshore median

9.1%

of hydrostatic · 0.0394 psi/ft

Near-vacuum wells

697

onshore, at extreme-low BHP

Offshore — US Gulf of Mexico

Over-pressured (HPHT / ultra-HPHT) · Lower Tertiary / Paleogene Wilcox. 10 Lower-Tertiary fields; 7 with a publicly disclosed reservoir pressure. Click the ⓘ on any row for the exact source. Fields with no published pore pressure show — (never a borrowed neighbour value).

Field	Operator	Water depth (ft)	Reservoir pressure (psi)	Equip rating (psi)	Temp (°F)	TVD (ft)	HPHT class
Anchor	Chevron	5,180	~25,000	20,000	275	30,000	ultra-HPHT
Anchor — source: OGJ 2024: initial reservoir (BHP) 23,000–27,000 psi — higher than the 20,000-psi equipment rating; 275F max flowing temp; pay 30,000–34,000 ft TVD (Wilcox 1–4).
Shenandoah	Beacon Offshore Energy	5,800	≥22,000	20,000	200	30,000	ultra-HPHT
Shenandoah — source: Clariant/World Oil: reservoir/formation pressures above 22,000 psi at ~200F (ultra-high-PRESSURE, moderate temp), ~30,000 ft TVD; 20,000-psi equipment rating separate.
Kaskida	BP	6,000	≥20,000	20,000	—	—	ultra-HPHT
Kaskida — source: AAPG: deep Wilcox is a '20,000 psi or higher' reservoir environment (matches the 20K equipment rating); JPT/BOEM: BP 20,000-psi FPU. Exact pore pressure not published — shown as ≥20,000.
Tiber	BP	4,132	up to 20,000	20,000	—	28,000	ultra-HPHT
Tiber — source: BP FID 2025 (Tiber-Guadalupe): reservoirs 'under pressures of up to 20,000 psi', Paleogene Wilcox; ~28,000 ft TVD. Temperature not field-specific.
Cascade/Chinook	MP Gulf of Mexico LLC (Murphy EXPRO)	8,200	~19,500	—	260	25,600	HPHT
Cascade/Chinook — source: OTC-24162/24163 + JPT: initial reservoir pressure ~19,500 psi, BHT ~256–260F, reservoir mid-point ~25,600 ft TVD.
Jack/St. Malo	Chevron	7,000	19,374	—	224	26,500	HPHT
Jack/St. Malo — source: Dice regional Wilcox reservoir study: Jack initial pressure 19,374 psi @ 224F, St. Malo 19,023 psi @ 225F; reservoir ~26,500 ft TVD.
Julia	ExxonMobil	7,000	~13,500^†	15,000	—	30,000	HPHT
Julia — source: Offshore Mag: subsea pressures ~13,500 psi (15,000-psi-rated trees + first permanent HIPPS); Hart Energy production test: 24.7°API oil.
Big Foot	Chevron	5,200	—	—	—	—	—
Big Foot — source: Wilcox oil field (Offshore Technology; Chevron). Field-specific reservoir pressure/temperature not publicly disclosed — shown as — rather than borrowed from neighbouring fields.
North Platte (renamed Sparta)	Shell	4,265	—	20,000	—	—	ultra-HPHT
North Platte (renamed Sparta) — source: World Oil/JPT: Sparta (ex-North Platte) is a 20,000-psi-rated development. All public '20,000 psi' figures are the equipment rating; true reservoir pore pressure not publicly disclosed — shown as —.
Stones	Shell	9,500	—	—	—	26,500	HPHT
Stones — source: Offshore Mag/S&D: Paleogene Wilcox, reservoir ~26,500 ft TVD (17,000 ft below mudline). Reservoir pressure/temperature not cleanly sourced — shown as —.

† Julia — Subsea system pressure (15,000-psi-rated trees + HIPPS), not a disclosed reservoir pore pressure.

Source: Public field disclosures (OGJ, OTC/JPT, OffshoreMag, operator releases); curated in worldenergydata reports/lower_tertiary/lifecycle/_facts.json

Onshore — US Mid-Continent

Under-pressured / near-vacuum. Top 40 fields by well count (of 178 ranked). Tier is coloured by field: severe mild normal; ⚠ flags fields containing near-vacuum wells.

OK 19,972 wellsKS 10,103 wellsTX 25 wells

Onshore aggregate: 30,100 wells · median BHP gradient 0.0394 psi/ft (≈9.1% of hydrostatic) · severe 28,316 · mild 814 · normal 970 · 697 near-vacuum · 178 fields ranked

Field	State(s)	Wells	Median BHP grad (psi/ft)	% hydrostatic	Near-vacuum	Earliest test yr	Tier
HUGOTON GAS AREA	KS	7,146	0.0316	7.3%	159 ⚠	1996	severe
MISSISSIPPIAN	OK	3,920	0.0609	14.1%	24 ⚠	2010	severe
WOODFORD	OK	3,705	0.1312	30.3%	5 ⚠	2010	severe
PANOMA GAS AREA	KS	2,342	0.0289	6.7%	20 ⚠	1996	severe
(unmatched)	KS,OK	1,306	0.0157	3.6%	15 ⚠	1996	severe
MISSISSIPPI LIME	OK	924	0.0234	5.4%	7 ⚠	2010	severe
CLEVELAND	OK	745	0.0944	21.8%	7 ⚠	2010	severe
HUNTON	OK	647	0.0731	16.9%	25 ⚠	2010	severe
TONKAWA	OK	466	0.0980	22.6%	2 ⚠	2010	severe
OSWEGO	OK	431	0.0348	8.0%	4 ⚠	2010	severe
MISSISSIPPI	OK	422	0.0487	11.2%	7 ⚠	2010	severe
MISSISSIPPIAN (LESS CHESTER)	OK	379	0.0858	19.8%	2 ⚠	2016	severe
CHEROKEE	OK	374	0.4090	94.5%	5 ⚠	2010	mild
BARTLESVILLE	OK	273	0.0822	19.0%	57 ⚠	2010	severe
MARMATON	OK	271	0.1336	30.9%	5 ⚠	2010	severe
SPRINGER	OK	255	0.3531	81.5%	0	2010	mild
DES MOINES	OK	243	0.2049	47.3%	1 ⚠	2010	severe
GREENWOOD GAS AREA	KS	233	0.0181	4.2%	51 ⚠	1996	severe
MISSISSIPPI SOLID	OK	221	0.1465	33.8%	4 ⚠	2010	severe
HUGOTON	KS	200	0.0352	8.1%	12 ⚠	1996	severe
DEESE	OK	196	0.0564	13.0%	24 ⚠	2010	severe
HOXBAR	OK	165	0.0915	21.1%	5 ⚠	2010	severe
SYCAMORE	OK	160	0.0931	21.5%	0	2010	severe
RED FORK	OK	152	0.1150	26.6%	5 ⚠	2010	severe
COTTAGE GROVE	OK	143	0.0888	20.5%	1 ⚠	2010	severe
MISSISSIPPI CHAT	OK	134	0.0482	11.1%	3 ⚠	2010	severe
SKINNER	OK	123	0.1297	30.0%	5 ⚠	2010	severe
CHESTER	OK	121	0.0263	6.1%	1 ⚠	2010	severe
VIOLA	OK	119	0.0628	14.5%	11 ⚠	2010	severe
MORROW	OK	112	0.0445	10.3%	4 ⚠	2010	severe
BROMIDE	OK	112	0.0912	21.1%	3 ⚠	2010	severe
DES MOINES GRANITE WASH	OK	98	0.1350	31.2%	0	2010	severe
DUTCHER	OK	93	0.1625	37.5%	7 ⚠	2010	severe
ATOKA	OK	88	0.0665	15.4%	0	2010	severe
WILCOX	OK	86	0.0596	13.8%	9 ⚠	2010	severe
MARCHAND	OK	81	0.0655	15.1%	0	2010	severe
CANEY	OK	77	0.1660	38.3%	0	2010	severe
MAYES	OK	73	0.0570	13.2%	0	2010	severe
DOUGLAS	OK	71	0.0250	5.8%	0	2010	severe
CROMWELL	OK	70	0.0753	17.4%	3 ⚠	2010	severe

Source: State well databases (Kansas KGS proration, Oklahoma OCC, Texas RRC); screened by worldenergydata underpressured_screen (BHP gas-column estimate → gradient tiers).

Roadmap — not yet screened

US GoM — non-LT playsNorway (Sodir) / UK (NSTA)Brazil (ANP) / Mexico (CNH)Texas RRC — full completion-packet screenColorado (ECMC)

Methodology

Offshore figures are public field disclosures (OGJ, OTC/JPT, OffshoreMag, operator releases) — disclosed reservoir (pore/BHP) pressures, distinct from the wellhead equipment rating; undisclosed values render —. Onshore figures come from state well databases (Kansas KGS, Oklahoma OCC, Texas RRC) screened by the worldenergydata underpressured_screen BHP gas-column estimate. Onshore is a depleted-era proxy — it measures economic operability at extreme-low bottomhole pressure in mature gas areas, not virgin sub-hydrostatic reservoirs. Hydrostatic reference: 0.433 psi/ft. Every number on this page traces to the committed _pressure.json.