A new report commissioned by the Northshore Business Council offers numbers to support a bit of conventional wisdom: The oil and gas industry is an important part of St. Tammany Parish’s economy, and it has only gotten more so in the past decade.

Since 2004, the year before Hurricane Katrina, the number of oil and gas companies in the parish has doubled, the number of their employees has increased sevenfold and their cumulative payroll has expanded by a factor of 15, the report says.

The report — prepared by Taimerica Management Co. — uses publicly available data for 2012 and 2013 from the U.S. Census Bureau, the U.S. Bureau of Labor Statistics, the Louisiana Workforce Commission and the U.S. Bureau of Economic Analysis to estimate the industry’s economic impact within the parish. The report does not project its potential future impact, including from the controversial plan to drill a hydraulic fracturing oil well near Mandeville.

In 2013, more than 7 percent of the total employment in the parish, or 5,900 workers, was in the oil and gas industry, the report says. Even more dramatically, 25 percent of the total payroll, or $900 million, was from oil and gas in 2012, and the industry accounted for 61 percent of the payroll growth in the parish since 2005, the report says.

St. Tammany has significant numbers of companies involved in both “upstream” and “midstream” oil and gas services, the report says.

“Upstream” functions are those focused mainly on oil and gas exploration and production, and St. Tammany had nearly as many active upstream companies, 48, as Orleans Parish, which had 60, the report says. “Midstream” services are those focused on transportation related to oil and gas production.

A third category, “downstream,” consists of refining, petrochemicals and other oil and gas products. The report lists no examples of downstream companies in St. Tammany Parish.

Much of St. Tammany’s oil and gas business is in support services that are office-based, the report says. While that may contribute to the parish’s image as a bastion of white-collar workers, it means the direct impact of those businesses is less than in places where there is significant drilling, gathering or production. Those activities help create more spin-off companies that add to the economy, the report says.

Also, a significant number of St. Tammany residents work in the oil and gas industry in adjacent parishes, the report says.

Northshore Business Council Executive Director Larry Rase said he hopes the report will remind residents of the importance of the industry to St. Tammany Parish.

“We just put this out to help people get the facts,” he said. “Oil and gas is very important to the economy.”

The Northshore Business Council is an invitation-only group of more than 50 presidents, CEOs and market managers centered along the Interstate 12 corridor in Tangipahoa, St. Tammany and Washington parishes. Its stated goal is to promote policies that enhance the quality of business and civic life through both advocacy and opposition, according to the organization’s website.

Follow Faimon A. Roberts III on Twitter, @faimon.