Once　gasoline　leaks　in　confined　spaces,　vapor-air　mixtures　with　concentration　gradients　will　form　above　the　liquid　surface　owing　to　evaporation,　and　explosion　may　occur　if　ignition　occurs　at　a　suitable　location.　This　study　aims　to　measure　the　concentration　gradient　of　gasoline　vapor-air　mixtures　and　to　investigate　the　effect　of　the　ignition　delay　(t(ig))　on　the　flame　behavior　and　overpressure　in　a　closed　duct.　The　results　reveal　that　the　flammable　layer　of　the　gasoline　vapor-air　mixtures　exist　only　at　a　certain　time　period.　After　ignition　of　the　stratified　vapor-air　mixtures,　a　blue　olive-shaped　premixed　flame　bubble　is　formed,　followed　by　a　bright　diffusion　flame　at　its　bottom,　and　subsequently,　two　symmetrical　eddies　form.　The　horizontal　speed　of　the　premixed　flame　tip　first　increases　to　approximately　3.5-4.3　m/s　and　then　decreases　to　1.5-2.0　m/s.　The　maximum　overpressure　of　the　current　stratified　gasoline-air　mixture　initially　increases　from　approximately　320　to　450　kPa　as　t(ig)　increases　from　6　to　10　min,　and　then　remains　nearly　unchanged　with　further　increase　in　t(ig).　A　maximum　value　of　450　kPa　is　obtained,　which　is　lower　than　the　results　of　homogeneous　gasoline-air　mixtures　in　previous　research.