TOKYO -- Prices for used oil tankers are soaring on high demand for vessels, as the military conflict between the U.S. and Iran forces shipping lines to bypass the Strait of Hormuz.

With shipbuilding capacity tight and delivery times growing longer, prices for 15-year-old vessels are now about 20% higher than those for new builds.

Overseas orders in the April-September period rose 3.6% on the year, according to data released Thursday by the Japan Ship Exporters' Association. Japanese shipbuilders' order backlogs have reached 29.91 million gross metric tons, equivalent to 3.5 years of output based on fiscal 2025 levels.

Contracts are already being signed for vessels scheduled for delivery beyond 2030, the association said.

Tight supply is not limited to Japan. Chinese shipbuilders, which hold more than half the global market, had order backlogs equivalent to seven years of 2025 output as of the end of June. As delivery times for new vessels lengthen, an unusual price inversion between new and used ships has emerged.

Five-year-old very large crude carriers (VLCCs) are priced at $215 million, while a 10-year-old vessel costs $190 million and a 15-year-old one $160 million, according to U.K.-based Clarksons Research.

All are more expensive than the $131 million price of a new build, with even 15-year-old vessels commanding a 22% premium.

Prices of secondhand tankers have climbed sharply since around June. Compared with January, prices for five-year-old vessels have risen by about 70%, while those for 10-year-old ones jumped 80% and 15-year-old ships 110%.

With the Strait of Hormuz still treacherous to navigate, countries that depend heavily on oil from the Middle East are stepping up efforts to secure alternative crude supplies.

Previously, crude oil could be transported through the Strait of Hormuz to Japan and other parts of East Asia in around 20 days. Procuring oil instead from the U.S. Gulf Coast takes more than 50 days for VLCCs, which cannot pass through the Panama Canal and must cross the Atlantic Ocean and sail around the Cape of Good Hope at the southern tip of Africa. The longer journeys have sharply increased demand for tankers.

A VLCC owned by Japanese shipping company Nippon Yusen, also known as NYK Line. (Nippon Yusen) Charter rates for tankers are also surging. The daily rate for a three-year VLCC charter stood at about $109,000 in October, nearly double that of January, according to Clarksons Research.

Shipowners want to capitalize on the current boom, but tankers are in short supply. Building vessels takes years, so owners have turned to used ships.

A Greek shipowner recently bought two 15-year-old VLCCs, according to U.K.-based Seasure Shipbroking. MarineNet, a Tokyo-based shipping information company, said that "demand is strong for used vessels that can be put into operation immediately while market conditions are favorable." Japan has traditionally relied on the Middle East for about 90% of its crude oil. In response to the latest crisis, the government is rushing to secure alternative suppliers and reduce that dependence. Similar moves are happening in other countries.

Demand to replace vessels that have exceeded their roughly 20-year service life is also expected to rise. Clarksons Research said in a report that demand to replace aging vessels and meet environmental requirements will underpin shipbuilding demand. For Japanese shipbuilders, the question is how much of that demand they can capture.

Japan aims to double domestic shipbuilding output from 2024 levels to 18 million gross tons in 2035. A government-created fund to revitalize the industry is supporting capacity increases, with combined public- and private-sector investment of about 900 billion yen ($5.69 billion).

Japan's shipbuilding industry held about half the global market in the 1970s, but its share has fallen to just over 10%. China, now the world's top shipbuilder, is moving to expand output further as it also races to capture growing demand.