What Is the Deepest Hole Ever Drilled?
"The deepest hole ever drilled" sounds like exactly the kind of fact that should be settled — one number, one hole, one record. It mostly is. But checking the primary sources behind it turned up something we didn't expect: the organization that actually keeps this record tells a noticeably different story than the science press that reports on it.
The claim
The Kola Superdeep Borehole, drilled by the Soviet Union on the Kola Peninsula in Arctic Russia, is the deepest hole ever drilled into the Earth — about 12,262 metres (over 7.6 miles) straight down — and drilling stopped in 1989 because the rock got too hot to continue.
Source trail
Drilling began on 24 May 1970 as a Soviet scientific program, not a commercial one — the goal was to sample the crust directly rather than extract anything. The project is decades over, so every current page about it is retelling a closed story, sourced back to two kinds of place: the official Guinness World Records entry for it, and independent science coverage (Scientific American, Interesting Engineering) plus Wikipedia's own compiled account. Checking those against each other is where the disagreement showed up.
Separately, "deepest" quietly gets confused with "longest" in casual retellings, because oil and gas wells drilled at a steep angle have gone farther along their own length without coming anywhere near as deep straight down — and the companies that drilled those wells publish their own numbers too.
What's confirmed
- Kola is still the deepest true-vertical hole ever drilled, and the record hasn't moved since it was set. Guinness World Records' own "Deepest penetration into the Earth's crust" page (checked 2026-08-17) currently lists the Kola Superdeep Borehole as the record holder, at 12,261 m (40,236 ft). Wikipedia's account (checked 2026-08-17) gives an almost identical figure, 12,262 m (40,230 ft), reached in 1989.
- Extreme heat genuinely stopped further drilling, at some point. Both independent accounts we fetched directly agree on this much: Scientific American and Interesting Engineering (both checked 2026-08-17) each state the rock at depth reached about 180°C (356°F) — roughly double what had been predicted — making it behave "more like plastic than rock" and deforming the drilling equipment.
- "Deepest" and "longest" are genuinely different records, and oil companies have broken the length one repeatedly using their own directly-published numbers. ExxonMobil's own investor press release (checked 2026-08-17) states its Odoptu OP-11 well, drilled off Sakhalin Island in January 2011, reached a total measured depth of 12,345 m (40,502 ft) — deeper along the pipe than Kola's vertical depth — while running mostly sideways rather than straight down. Rosneft's own press release (checked 2026-08-17) states a later well in the same Sakhalin-1 project reached a horizontal-completion length of 15,000 m by 2017. Neither well comes close to Kola's vertical depth; both are longer measured along their own path.
What isn't confirmed
- Guinness's own record page tells a materially different story than the science press does, and we could not find anywhere that reconciles the two. Guinness states work "continued until 1983," stopped "due to lack of funds," at a rock temperature of 210°C (410°F). Scientific American and Interesting Engineering both instead describe drilling halting around 1992 because of 180°C heat — a decade later, a different stated cause, and a temperature 30°C lower than Guinness's own figure. We checked both kinds of source directly and they simply don't agree; nothing we found addresses the gap.
- Wikipedia's fuller account complicates the tidy "stopped in 1989 because it got too hot" story that most casual pages repeat. Per Wikipedia, 12,262 m was the maximum depth reached by one branch of the hole in 1989; a separate fourth branch was halted in 1992 specifically because of 180°C heat; and the project as a whole didn't end until 1995, when Wikipedia states funding — not temperature — is what finally stopped it. We could not verify Wikipedia's own cited sources for these later dates directly this session, so this more granular account is reported as Wikipedia's claim, cross-checked only against the two independent outlets above, not independently confirmed beyond that.
- Casual "world's deepest hole" claims routinely don't say which record they mean. A headline calling an oil well the "world's deepest" or "world's longest" hole, without specifying vertical depth versus measured length along the bore, is easy to read as challenging Kola's record when it isn't — the wells above are longer, not deeper.
Verdict
The headline claim holds: Kola is the deepest hole ever drilled by true vertical depth, and that hasn't changed since the 1980s. What doesn't hold up as cleanly is the story behind why drilling stopped — the record-keeping organization's own page and the independent science coverage disagree with each other on the year, the cause, and the temperature, and neither matches the more granular multi-branch, multi-year account Wikipedia gives. On top of that, the "deepest" record and the "longest" record are two different things that oil-industry press releases keep breaking separately, and casual coverage blurs the two more often than it distinguishes them.