diff --git a/code/_onclick/hud/screen_objects.dm b/code/_onclick/hud/screen_objects.dm
index 4ca8f9f5d75..ed054ae6c8a 100644
--- a/code/_onclick/hud/screen_objects.dm
+++ b/code/_onclick/hud/screen_objects.dm
@@ -276,37 +276,79 @@
 							C << "<span class='notice'>You are not wearing a mask.</span>"
 							return 1
 						else
-							if(istype(C.l_hand, /obj/item/weapon/tank))
-								C << "<span class='notice'>You are now running on internals from the [C.l_hand] on your left hand.</span>"
-								C.internal = C.l_hand
-							else if(istype(C.r_hand, /obj/item/weapon/tank))
-								C << "<span class='notice'>You are now running on internals from the [C.r_hand] on your right hand.</span>"
-								C.internal = C.r_hand
-							else if(ishuman(C))
+							var/list/nicename = null
+							var/list/tankcheck = null
+							var/breathes = "oxygen"    //default, we'll check later
+							var/list/contents = list()							
+
+							if(ishuman(C))
 								var/mob/living/carbon/human/H = C
-								if(istype(H.s_store, /obj/item/weapon/tank))
-									H << "<span class='notice'>You are now running on internals from the [H.s_store] on your [H.wear_suit].</span>"
-									H.internal = H.s_store
-								else if(istype(H.belt, /obj/item/weapon/tank))
-									H << "<span class='notice'>You are now running on internals from the [H.belt] on your belt.</span>"
-									H.internal = H.belt
-								else if(istype(H.l_store, /obj/item/weapon/tank))
-									H << "<span class='notice'>You are now running on internals from the [H.l_store] in your left pocket.</span>"
-									H.internal = H.l_store
-								else if(istype(H.r_store, /obj/item/weapon/tank))
-									H << "<span class='notice'>You are now running on internals from the [H.r_store] in your right pocket.</span>"
-									H.internal = H.r_store
+								breathes = H.species.breath_type
+								nicename = list ("suit", "back", "belt", "right hand", "left hand", "left pocket", "right pocket")
+								tankcheck = list (H.s_store, C.back, H.belt, C.r_hand, C.l_hand, H.l_store, H.r_store)
 
-							//Seperate so CO2 jetpacks are a little less cumbersome.
-							if(!C.internal && istype(C.back, /obj/item/weapon/tank))
-								C << "<span class='notice'>You are now running on internals from the [C.back] on your back.</span>"
-								C.internal = C.back
+							else    
 
+								nicename = list("Right Hand", "Left Hand", "Back")
+								tankcheck = list(C.r_hand, C.l_hand, C.back)
+
+							for(var/i=1, i<tankcheck.len+1, ++i)
+								if(istype(tankcheck[i], /obj/item/weapon/tank))
+									var/obj/item/weapon/tank/t = tankcheck[i]
+									if (!isnull(t.manipulated_by) && t.manipulated_by != C.real_name && findtext(t.desc,breathes))
+										contents.Add(t.air_contents.total_moles)	//Someone messed with the tank and put unknown gasses
+										continue					//in it, so we're going to believe the tank is what it says it is
+									switch(breathes)					
+																		//These tanks we're sure of their contents
+										if("nitrogen") 							//So we're a bit more picky about them.
+											
+											if(t.air_contents.nitrogen && !t.air_contents.oxygen)
+												contents.Add(t.air_contents.nitrogen)
+											else
+												contents.Add(0)	
+
+										if ("oxygen")
+											if(t.air_contents.oxygen && !t.air_contents.toxins) 
+												contents.Add(t.air_contents.oxygen)
+											else
+												contents.Add(0)
+
+										// No races breath this, but never know about downstream servers.
+										if ("carbon dioxide")
+											if(t.air_contents.carbon_dioxide && !t.air_contents.toxins)
+												contents.Add(t.air_contents.carbon_dioxide)
+											else
+												contents.Add(0)
+										
+	
+								else									
+									//no tank so we set contents to 0
+									contents.Add(0)
+
+							//Alright now we know the contents of the tanks so we have to pick the best one.
+
+							var/best = 0
+							var/bestcontents = 0
+							for(var/i=1, i <  contents.len + 1 , ++i)
+								if(!contents[i])
+									continue	
+								if(contents[i] > bestcontents)
+									best = i
+									bestcontents = contents[i]
+							
+							
+							//We've determined the best container now we set it as our internals
+
+							if(best)
+								C << "<span class='notice'>You are now running on internals from [tankcheck[best]] on your [nicename[best]].</span>"
+								C.internal = tankcheck[best]
+							
+								
 							if(C.internal)
 								if(C.internals)
 									C.internals.icon_state = "internal1"
 							else
-								C << "<span class='notice'>You don't have an oxygen tank.</span>"
+								C << "<span class='notice'>You don't have a[breathes=="oxygen" ? "n oxygen" : addtext(" ",breathes)] tank.</span>"
 		if("act_intent")
 			usr.a_intent_change("right")
 		if("help")
diff --git a/code/game/machinery/atmoalter/canister.dm b/code/game/machinery/atmoalter/canister.dm
index 1d5f210dd33..d8b85211501 100644
--- a/code/game/machinery/atmoalter/canister.dm
+++ b/code/game/machinery/atmoalter/canister.dm
@@ -255,6 +255,8 @@ Release Pressure: <A href='?src=\ref[src];pressure_adj=-1000'>-</A> <A href='?sr
 
 		if (href_list["remove_tank"])
 			if(holding)
+				if(istype(holding, /obj/item/weapon/tank))
+					holding.manipulated_by = usr.real_name
 				holding.loc = loc
 				holding = null
 
diff --git a/code/game/objects/items/devices/PDA/PDA.dm b/code/game/objects/items/devices/PDA/PDA.dm
index 9123617f2a7..2750af1b05b 100755
--- a/code/game/objects/items/devices/PDA/PDA.dm
+++ b/code/game/objects/items/devices/PDA/PDA.dm
@@ -1042,6 +1042,9 @@ var/global/list/obj/item/device/pda/PDAs = list()
 
 		if(5)
 			if((istype(A, /obj/item/weapon/tank)) || (istype(A, /obj/machinery/portable_atmospherics)))
+				if(istype(A, /obj/item/weapon/tank))
+					var/obj/item/weapon/tank/t = A
+					t.manipulated_by = user.real_name
 				var/obj/icon = A
 				for (var/mob/O in viewers(user, null))
 					O << "\red [user] has used [src] on \icon[icon] [A]"
diff --git a/code/game/objects/items/weapons/tanks/tanks.dm b/code/game/objects/items/weapons/tanks/tanks.dm
index 143ff13a041..e0e30e60cb9 100644
--- a/code/game/objects/items/weapons/tanks/tanks.dm
+++ b/code/game/objects/items/weapons/tanks/tanks.dm
@@ -15,7 +15,8 @@
 	var/distribute_pressure = ONE_ATMOSPHERE
 	var/integrity = 3
 	var/volume = 70
-
+	var/manipulated_by = null		//Used by _onclick/hud/screen_objects.dm internals to determine if someone has messed with our tank or not.
+						//If they have and we haven't scanned it with the PDA or gas analyzer then we might just breath whatever they put in it.
 /obj/item/weapon/tank/New()
 	..()
 
@@ -86,7 +87,7 @@
 			O << "\red [user] has used [W] on \icon[icon] [src]"
 
 		var/pressure = air_contents.return_pressure()
-
+		manipulated_by = user.real_name			//This person is aware of the contents of the tank.
 		var/total_moles = air_contents.total_moles()
 
 		user << "\blue Results of analysis of \icon[icon]"
@@ -261,4 +262,4 @@
 			integrity--
 
 	else if(integrity < 3)
-		integrity++
\ No newline at end of file
+		integrity++