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Vance says his company has been producing an asphalt-based sealer for more than 10 years and in that time has seen the quality of the industry's asphalt emulsion sealers improve.

"Asphalt sealers are better than they were before but they're still a little lacking relative to coal tar," Vance says. "There's a reason coal tar has been made all these years: It works better and asphalt emulsion has some deficiencies."

Chris Mariani, vice president of marketing for GemSeal, says the company produces an asphalt-based sealer at its Tampa location and could expand production of that product to other GemSeal locations if coal tar availability becomes an issue this year.

"What defines 'better'?" Mariani asks. "Pretty much everyone wants a sealer they can depend on to provide a consistent level of durability and aesthetic enhancement for the parking lot. Asphalt-base sealers can provide that, but coal tar does a better job of both in the long term. With today's technology, we're not going to expect an asphalt-based sealer to go mile for mile with a coal tar emulsion. That may change in the future"

Mariani says GemSeal's asphalt-based sealer is polymer modified and it can be diluted up to 25% with water, but because it contains polymers it is more expensive then non-polymer-modified asphalt sealers.