Video: Ignitable drinking water from a well in Candor, New York, located above the Marcellus Shale Formation.

Hundreds of cases of water pollution from oil or gas drilling have been confirmed by several states, according to data obtained by the Associated Press. The pollution comes from both hydraulic fracturing (fracking) and conventional drilling methods to extract petroleum and natural gas. Pennsylvania alone confirmed 106 instances of pollution out of 5,000 new wells drilled since 2005. Ohio, Texas, and West Virginia also confirmed pollution in reports of varying detail:

Among the findings in the AP's review:

— Pennsylvania has confirmed at least 106 water-well contamination cases since 2005, out of more than 5,000 new wells. There were five confirmed cases of water-well contamination in the first nine months of 2012, 18 in all of 2011 and 29 in 2010. The Environmental Department said more complete data may be available in several months. — Ohio had 37 complaints in 2010 and no confirmed contamination of water supplies; 54 complaints in 2011 and two confirmed cases of contamination; 59 complaints in 2012 and two confirmed contaminations; and 40 complaints for the first 11 months of 2013, with two confirmed contaminations and 14 still under investigation, Department of Natural Resources spokesman Mark Bruce said in an email. None of the six confirmed cases of contamination was related to fracking, Bruce said. — West Virginia has had about 122 complaints that drilling contaminated water wells over the past four years, and in four cases the evidence was strong enough that the driller agreed to take corrective action, officials said. — A Texas spreadsheet contains more than 2,000 complaints, and 62 of those allege possible well-water contamination from oil and gas activity, said Ramona Nye, a spokeswoman for the Railroad Commission of Texas, which oversees drilling. Texas regulators haven't confirmed a single case of drilling-related water-well contamination in the past 10 years, she said.

The report notes that beginning in 2011, "the Pennsylvania Department of Environmental Protection aggressively fought efforts by the AP and other news organizations to obtain information about complaints related to drilling. The department has argued in court filings that it does not count how many contamination "determination letters" it issues or track where they are kept in its files."

Some experts have said that people who are trying to understand both the benefits and harms from the fracking/drilling boom need "comprehensive details about complaints, even if some cases are from natural causes."

A positive note about the state of Texas, contrasting the limited amount of information available from Pennsylvania: "Texas officials supplied a detailed 94-page spreadsheet almost immediately, listing all types of oil and gas related complaints over much of the past two years. The Texas data include the date of the complaint, the landowner, the drilling company and a brief summary of the alleged problems. Many complaints involve other issues, such as odors or abandoned equipment."

"If the industry has nothing to hide, then they should be willing to let the facts speaks for themselves," Scott Anderson, an expert on oil and gas drilling with the Environmental Defense Fund, a national nonprofit based in Austin, said. "The same goes for regulatory agencies."