The new e-cigarette industry is still tiny, with global sales this year of $5 billion compared with more than $800 billion for tobacco products, according to estimates by Wells Fargo Securities. Still, cigarette companies have hedged their bets by acquiring e-cigarette makers or stepping up their own research efforts.

Along with replicating important sensory aspects of smoking, like taste, the biggest hurdle for the new devices, experts say, is delivering nicotine with the efficiency of a cigarette. Within seconds of taking a drag, a smoker feels the nicotine’s soothing effects because compounds that are produced when tobacco burns are perfectly sized to carry nicotine deep into the lungs allowing the drug to quickly reach the brain. Those same compounds, which are collectively known as tars, also cause cancer and other diseases.

By comparison, the type of vapor generated by e-cigarettes, experts say, is a less efficient carrier of nicotine than smoke. “There is more deposition in the mouth,” with vapor, said Jeffrey S. Gentry, the chief scientific officer of R.J. Reynolds, a division of Reynolds American.

A study published last year showed that one e-cigarette brand, Njoy, produced levels of nicotine in a user’s blood significantly lower than the amount produced by a cigarette like a Marlboro. As a result, e-cigarette users have frequently turned to larger devices known as vape pens that have bigger batteries that can produce more heat. But more heat to increase nicotine levels may also result in higher levels of toxins and carcinogens, experts say.

Tobacco companies have rushed to increase nicotine levels in their vapor devices.

About a year after Altria, which sells Marlboro, introduced the MarkTen e-cigarette brand, it increased the concentration of nicotine by about 65 percent. Blu eCigs, which is owned by Lorillard, has raised the nicotine output of its latest device by 50 percent through a variety of changes such as increasing its nicotine concentration and incorporating a larger battery to produce higher heat. Njoy, which only makes e-cigarettes, is using a pharmaceutical ingredient in a new version of its device that is supposed to increase vapor absorption in the lung and elevate nicotine delivery to about 70 percent of a cigarette, according to company data.

At Philip Morris International’s research center here, where about 300 scientists work, the nicotine chase is headed in several directions. The company says it has spent about $2 billion since 2008 researching cigarette alternatives with much of that effort focused on devices that use tobacco, but heat it, rather than burn it. Though the “safer” cigarettes that Philip Morris and R.J. Reynolds introduced decades ago were also heat-not-burn devices — and flopped with smokers — the new products, Philip Morris officials say, are more technologically advanced.