BENGALURU - With Indian COVID-19 patients struggling to find medical oxygen in the middle of a second deadly wave of coronavirus infections, shares in companies that produce the gas — or simply have it in their names — are rallying.

Bombay Oxygen, National Oxygen Ltd and Bhagawati Oxygen Ltd — all tiny firms not listed on any major stock index — have surged 47% or more in April, a period in which India's broader market has slumped 2%.

Over the past few days, India has ramped up oxygen production nationwide as supplies of the gas have fallen short and infections surge. Hospitalised COVID-19 patients who are seriously ill often need supplemental oxygen to increase its supply in the blood and lungs.

Meanwhile, prices for oxygen cylinders in many parts of the country have more than doubled.

National Oxygen and Bhagawati Oxygen produce industrial gases including oxygen, but Bombay Oxygen ended its gas operations in 2019 and is now a non-bank lender, according to its latest annual report.

Formerly known as Bombay Oxygen Corp Ltd, it is now Bombay Oxygen Investments Ltd. Its shares have climbed 112% since the start of April. They fell 5% on Tuesday.

A portion of Bombay Oxygen's website, however, still says it makes oxygen and other industrial gases. Reuters could not reach company representatives for comment.

"Once COVID-19 cases start going down, and oxygen supplies go up, the prices will come to normal levels and the stocks should go back (to earlier levels)," said Rusmik Oza, senior vice-president at Kotak Securities in Mumbai.

Shares in notable gas producers like Linde India Ltd , the local partner of the U.S.-German industrial gas maker Linde, have more than doubled since the end of January, around the time India's second wave of COVID-19 infections began.

Petrochemicals companies including Reliance Industries Ltd and Indian Oil Corp have begun supplying medical oxygen to plug the shortage. Shares in both companies are down about 4% each this month.

Shares of Gagan Gases Ltd, a distributor of fuel gas commonly known as LPG, have also climbed 47% this month - despite not having any significant news. A Gagan plant manager said the company does not produce oxygen. Reuters could not reach other representatives for comment.

It may be a case of success by association, but it is also short-lived.

"It's an opportunistic, tactical trade," Kotak's Oza said.

(Reporting by Sachin Ravikumar in Bengaluru; Editing by Bernard Orr) ((saisachin.r@tr.com; +91 80 6182 2754; Twitter: @sachinr27))